rolex screw down crown - welcome to the nawcc! · n 1926 rolex created the waterproof rolex oyster...

NAWCC Watch & Clock Bulletin • December 2010 • 677www.nawcc.org

In 1926 Rolex created the waterproof Rolex Oyster wrist-watch (Figure 1). In 1927 Mercedes Gleitze became the fi rst British woman to swim the English channel; she subse-

quently tried (unsuccessfully) to repeat the feat wearing a Rolex Oyster, but the watch survived the event unscathed! In Novem-ber 1927 Hans Wilsdorf, cofounder and managing director of Rolex, featured Miss Gleitze and the Rolex Oyster in an entire front page ad of the Daily Mail newspaper to, as Wilsdorf later wrote, “proclaim the success of the fi rst waterproof watch.”1 Wilsdorf went on: “This was the fi rst step in the triumphant rise to fame of the Rolex Oyster.” And the rest, as they say, is history. Or is it?

I am sure that if a survey asked who invented the waterproof watch, the majority would reply Rolex. But is this because it is true, or is it be-cause of successful marketing by Wilsdorf and Rolex? I believed the simple story of how Rolex invented the waterproof watch until I began researching this article. So although the article is principally about the Rolex screw down crown, the break-through that made the waterproof Oyster wristwatch possible, I begin by going back in time to review some previous attempts to make watches dustproof and waterproof, and in particular some earlier screw down crowns.

Before I begin to get into depth in this article, I should perhaps ex-plain what is meant by a screw down

crown and why it is signifi cant. A common crown that one encoun-ters most often and that is not screw down generally occupies two posi-tions: (1) Its normal position next to the watch when it can be turned to wind the watch; and (2) a pulled-out position, which when turned will set the hands. Sometimes there are other pulled-out positions for set-ting the date, etc.

The unusual part about a screw down crown is that in its normal po-sition, next to the case, it is screwed down onto a threaded part of the case, so that some part of it clamps down onto a part of the case and makes a waterproof seal. To do any of the normal winding and setting actions, the wearer must fi rst un-screw the crown, breaking the seal.

Figure 1. 1927 gold Rolex Oyster.

PHOTO BY AND © OLDETIMERS.COM.

by David Boettcher (ENG)

Once the crown has been unscrewed from the case, it usually springs free and engages with the winding stem, so that the watch can be wound and the hands set, etc. After the winding and setting is complete, the crown must be screwed back onto the case to restore the waterproof seal.

Early Improved Watch Cases

Early attempts to make watches waterproof, or at least dustproof,

revolved around the joints of the case back, which was traditionally a snap closed design, sometimes with an ad-ditional inner cover or cuvette, and the bezel, which carries the glass or crystal. These joints were an obvious route for dust and moisture to enter the case.

Improved watch cases where the case back and bezel screw onto the middle part of the case were being made in America by Fahys in the latter part of the ninetenth century, and in Europe there was the Borgel case. Designed by Francois Borgel of Geneva, the Borgel case has no sepa-rate back: the movement, bezel, and crystal are all carried on a threaded ring that screws into the case from the front.

The Rolex Screw Down Crown

(and its antecedents)

A tale of three patents, and a few more!

© 2010 National Association of Watch and Clock Collectors, Inc. Reproduction prohibited without written permission.

678 • December 2010 • NAWCC Watch & Clock Bulletin www.nawcc.org

The Invention of theScrew Down Crown

But these improved case designs all still had a weak point: the

winding button or crown, and the stem, the shaft that carries the action of turning the crown into the move-ment. The winding stem must pass from the crown through the watch case and into the movement, and it must be free to turn and slide as the watch is wound and set, so there must be clearance around the stem, along which moisture and dust can enter the case and penetrate to the very heart of the movement.

Early attempts to seal the crown/ stem opening were made by fi tting a cap over the crown which screwed down onto the pendant, the tube projecting from the case of a pocket watch that carries the stem, crown, and the bow by which the watch is at-tached to a chain for safety. Watches with these caps are called “explorers watches” for obvious reasons, but the separate cap, which was fi ddly to use and easy to lose, was not very practi-cal for everyday use.

Ezra C. Fitch U.S. PatentNo. 237,377, 1881

Ezra C. Fitch of New York was a prolifi c inventor who was award-

ed numerous patents between 1872 and 1914, including in 1879 a patent for a removable screw cap enclosing the crown of a pocket watch to pre-vent the entry of dust or water. In 1881 Fitch obtained a patent on an invention that did away with the in-convenience of the removable cap. Instead of a separate cap that screwed down and enclosed the crown, he made the crown itself also function as a cap (Figure 2). In Fitch’s design the crown is threaded internally and screws down onto an external thread on the pendant. I will let Fitch him-self introduce the concept to you:

“My present invention is partly related to former patents issued to me April 22 and October 2, 1879, the former of which shows a remov-able screw-cap screwing tightly upon the stem and inclosing the crown or winding-knob, while the latter shows

a form of key similar to what I now employ. My present invention, how-ever, is mainly distinguished by form-ing the crown or winding-knob to act as a screw-cap and to screw directly upon the [pendant], so that by turn-ing the crown or knob in one way the knob may be screwed tightly to its seat, and by turning it in the opposite direction the watch may be wound, so that by this means the construc-tion is simplifi ed and the advantage of an air-tight stem is secured, while the watch may be wound as quickly and easily as is the case with the com-mon stem-winding crown.”

A screw thread alone does not guarantee a watertight joint, the small clearances that are necessary between the threads of the two parts forming effectively a long narrow tube. In Figure 2, it can be seen that when the crown is fully screwed down, the base of the crown will meet shoulder “e” on the pendant, forming a tight joint. If the base of the crown and the shoulder “e” were well made and fi nished, then a dust-tight and watertight joint would have been achieved. It is not neces-sary to have a gasket to achieve a wa-tertight joint: gaskets simply make it easier to achieve a seal if the mating faces are not perfectly fl at and paral-lel, at the expense of introducing an extra component that can age, dete-riorate, and fail. For a joint that is go-ing to be undone every day, especial-ly a screwed joint where the gasket will be subject to sliding as well as compression, a small delicate gasket made of the typical gasket materials that were available at the time, such

as leather or cork, is not an ideal in-clusion, and a metal to metal joint as in Fitch’s design is a better solution. My only criticism of this joint is that it is in an exposed position and could have been vulnerable to damage and dust. I am not sure how well these joints could have been made by the machinery and techniques available at the time, and I have not seen any reports of their watertightness in practice. I would be very interested to receive any such information.

The screw thread is left-handed so that the action of unscrewing the crown also winds the movement. As Fitch says in the patent, “when the [crown] is turned in the direction to wind the watch the [crown] un-screws from the [pendant] and freely permits the winding motion. To wind the watch, therefore, it is only necessary to unscrew the [crown] one or two turns, so as to allow the [crown] suffi cient back play on the [pendant] without bringing it to a seat on the shoulder, and the wind-ing of the movement may then be accomplished with the usual back-and-forth rotation of the [crown] in as quick and easy a manner as with the usual stem-winding crown. When the winding is completed the [crown] may be screwed tightly to its seat on the stem by a slight continu-ation of the back movement, thus ef-fectually preventing the entrance of dust or moisture through the stem.”

Fitch obviously envisaged that it would not be necessary to unscrew the crown completely to wind the watch (although the watch would wind normally in the fully unscrewed

Figure 2. Fitch’s patent screw down crown.



position) but just enough to allow the usual back-and-forth rotation of the crown. This was presumably to reduce the perceived burden on the wearer of unscrewing the crown fully. But I wonder about the implica-tions of this for wear of the threads in the crown and on the pendant.They were not lubricated, and I can envisage these threads wearing quite quickly, particularly on a silver case. It was partly concerns about wear of these threads that caused Rolex to in-troduce automatic winding.

Fitch’s design also included a slid-ing joint that allowed some relative axial movement of the crown and that part of the stem Fitch calls the key. The key, item “d” in Figure 2, engages with the winding mecha-nism in the watch movement. Fitch describes the axial movement as necessary so that when the crown is screwed down, the key can be moved outward against a spring to allow the movement to be swung into or out of the case.

To achieve this axial movement, the outer end of the key is square in section, and the neck of the crown has a square bore into which the square section of the key fi ts, thus forming a fi xed rotational connection between crown and key, but allowing the key and the crown to slide freely relative to each other in the axial direction. To couple the crown and key togeth-er so that they don’t become disen-gaged, a slot “f” is formed in the key and a small screw or pin, “g,” is in-serted through the neck of the crown, projecting into the slot and forming a stop against each end.

Hand-setting, and therefore the interaction of the stem/key with the keyless mechanism, is not mentioned in this patent by Fitch. The keyless mechanism determines whether ro-tation of the crown winds the main-spring or sets the hands, and in pen-dant- or stem-set watches the mech-anism is moved from the winding position to the hand-set position by pulling out the crown.

The design given in the patent would have worked with pin-set or lever-set movements, where a pin is pressed or a lever is moved to change the keyless mechanism from the

winding to the hand-setting posi-tion and the crown does not need to be moved. However, I have been in-formed that Fitch’s design did work with stem-set movements such as the 1883 open-face Waltham where it will wind and set as normal. Per-haps this was a later development or a modifi cation to Fitch’s design that included a detent sleeve.

Unlike European watches, Ameri-can pocket watch movements and cases were usually designed to be in-terchangeable and sold separately, so that a customer could choose a move-ment and case combination to suit his taste and his budget. Stem-set cas-es generally included a detent sleeve, which holds the stem in either of two positions: crown in for winding and normal use, and crown out for hand-setting. Stem-set movements to fi t these cases have a negative set keyless mechanism, which a spring shifts to the setting position if the stem is not holding it in the winding position.

It is possible that if the crown of Fitch’s design, as described in this pat-ent, were unscrewed and then pulled out so that the key “d” was with-drawn against its spring, this would have allowed a negative set keyless mechanism to adopt the hand-set position. But Fitch describes pulling the key out like this, to the full extent allowed by its spring, as being used to disengage the stem to allow the movement to be swung into or out of the case, so it would appear that he had not considered stem-setting as part of this patent.

In addition to the, admittedly small, inconvenience of having to unscrew the crown to wind the watch, there was anoth-er drawback to Fitch’s screw down crown design that would have acted against its widespread uptake. The thread was made left-handed so that when the watch was fully wound, the crown could be screwed down using the ratchet on the mainspring barrel. This is the ratchet that

allows winding to be accomplished, as Fitch says, “with the usual back-and-forth rotation of the crown.” The “forth” part winds the spring, and the “back” part is the series of little ratchet clicks that you hear when you roll the crown back, which allows the winding stem to be freely reversed ready for another forward winding movement.

When the watch is fully wound, the crown can no longer be rotated forward, and the left-hand thread allows it then to be screwed down backward onto the pendant. But this feature is also a problem. If the watch is fully wound and the owner screws the crown down and then notices that the hands need to be set to the correct time, he is in a pickle. The crown can no longer be unscrewed, because the spring is fully wound! He must wait until the watch has run down somewhat before he can un-screw the crown to set the hands.

Watch cases with screw down crowns like this were produced in small numbers by the American Watch Company of Waltham in the 1880s. Figure 3 by Jerry Treiman is a picture of such a watch. The crown is partly unscrewed and the left-hand screw thread can clearly be seen.

Interestingly, Ezra C. Fitch became president of the American Watch Company in 1883, so he obviously had a personal interest in seeing his own patented ideas put into prac-tice. The American Watch Company shut down the case department in Waltham in the mid-1880s, so Fitch’s direct interest in the manufacture of

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Figure 3. American Watch Co. screw down crown.



these designs was relatively short-lived.

The design doesn’t seem to have achieved great commercial or popu-lar success, however dusttight or wa-tertight it was. The working environ-ment for a pocket watch is relatively benign, tucked away in a warm dry pocket, only pulled into the outside world occasionally when its owner wants to know the time, so perhaps the extra complication wasn’t found to be necessary or worthwhile by the watch-buying public.

Almon Twing U.S. PatentNo. 243,011, 1881

At virtually the same time that Fitch was registering his patent,

another inventor, Almon Twing of Waltham, was also registering a pat-ent for a screw down crown. Like Fitch, Twing recognized that using a loose dust cap to cover the crown was an inconvenient arrangement and envisaged using the crown it-self as the dust cap, screwing down onto the pendant to form a dust-proof seal. But Twing went further than Fitch and incorporated a clutch into the crown and winding stem assembly. This was arranged so that, when the crown was in position to screw down onto the pendant, it was free to turn on the winding stem, but when the crown was unscrewed from the pendant, it was brought into engagement with the winding stem.

Figure 4 shows how Twing achieved this coupling and de-coupling. Part g is a collar that sits around the winding stem. It is fas-tened securely into the end of the bore of the crown, so that the crown and collar are fi xed together. Part f is a pin that is fi xed through the end of the winding stem. The collar has two radial slots cut into it on opposing sides, the same size as the diameter of the pin.

Figure 4 (fi g. 5) of the patent shows the crown is in position to screw down on the pendant. In this position pin f is clear of the collar (g) and the crown can turn freely without turning the winding stem. Figure 4 (fi g. 6) of the patent shows

the crown unscrewed from the pen-dant. The spring forces the collar and crown away from the watch case, and pin f drops into the slots in the collar, coupling the crown and stem.

The Twing patent is surprisingly advanced in its conception, com-prising all the features necessary for a successful screw down crown. The clutch allowed the use of a normal right-hand thread for the crown and pendant and allowed the crown to be screwed and unscrewed even if the watch was fully wound. But it ap-pears that it was never actually used on a watch. Perhaps without having Fitch’s infl uence, any manufacturer that Twing approached with his in-vention would recognize that it was a solution in search of a problem, and not a commercial proposal.

Gilbert Dennison BritishPatent No. 1390, 1915

The Fitch design seems to have slipped into obscurity, or at least

not been widely known outside America, because in 1915 Gilbert Dennison, of the Dennison Watch Case Company of Birmingham, Eng-land, and grandson of Aaron Lufkin Dennison, obtained a British patent on a screw down crown very simi-lar to Fitch’s design, left-hand screw thread and all (Figure 5), although Fitch’s patent is not mentioned ex-plicitly in Dennison’s patent. Den-nison does describe a prior patent

where the pendant has an internal screw thread and two “annular seat-ing surfaces engaged by correspond-ing surfaces formed on the [crown],” the crown presumably having an external thread to engage with the pendant. That patent design sounds very different from Fitch’s and is un-known to me.

The principal difference from Fitch’s patent is that Dennison envis-aged a fl exible packing, shown as item 1 in Figure 5, to make the watertight joint between the crown and the pendant. Although the Fitch patent would have lapsed by 1915, it seems unlikely that this small difference would have enabled Dennison to ob-tain a patent without reference to the Fitch patent, unless Fitch’s patent and

Figure 4. Almon Twing Patent 1881.

Figure 5. Dennison’s 1915 patent.



watches made to its design were not known to the British patent examin-er, and there was no public objection when the patent was published.

Dennison’s design worked in ex-actly the same way as Fitch’s design, and it had the same drawback with re-gard to setting the hands if the watch was fully wound. But the drawing does include a detent sleeve, shown as item 6 in Figure 5, so it must have been intended to be used with stem- set watches. Dennison does not de-scribe in detail how he envisaged his invention being used in practice, and in particular he makes no mention of how the extra axial movement of the crown being unscrewed and screwed down would be accommodated by the keyless mechanism.

The principal problem with Den-nison’s patent would be fi nding the “suitable material” for the packing disk, which Dennison describes but does not name. Packing materials available at the time such as leather, cork, or string loaded with graphite, were not very suitable for this applica-tion, which is perhaps why the design seems to have never actually been used on a Dennison watch case.

Charles L. DepollierU.S. Patent No.1,292,441, 1919

Another watch case design was the Depollier wristwatch made

by Jacques Depollier & Son. This was the subject of a U.S. patent issued to Charles L. Depollier on January 28, 1919, No. 1,292,441. In this design the crown has a slotted tapered skirt that bayonet locks in a quarter of a turn or so under lugs on the side of the case, pressing down onto a gasket. One of these watches was worn by Roland Rohlf during a record altitude fl ight of 34,610 feet on September 18, 1919, in a Curtiss K-12. Advertise-ments celebrating this achievement not only claimed that it was water-proof but that it even maintained the atmospheric pressure inside the case against the rarefi ed atmosphere of the high altitude!

I am dubious about how durable the bayonet-locking mechanism would have proved against wear, remem-

bering that it needed to be undone every day to wind the watch. It also has little scope to cope with changes in thickness of the gasket material (e.g., as it ages and compresses). The diffi culty of fi nding a suitable gasket material would have been a problem. It seems that cork was used, which I expect would have proved unsatisfac-tory after a fairly short time. Cork is a good material to use for the stoppers of wine bottles, provided the bottle is stored on its side so that the cork never dries out; cork is also good for joints that are rarely disturbed, with the gasket being replaced each time. But in this application I would ex-pect the tiny cork gasket to dry out, become hard and brittle, and even-tually disintegrate as the crown was turned. These watches seem to have been produced only for a short while and are very rare and seem to have slipped quickly into obscurity.

Patent Protection

As we will shortly see, the screw down crown was a vital part of

the success of the waterproof Rolex Oyster. The screw down crown had been invented in America by Fitch, and it seems also simultaneously and independently by Twing, and per-haps again by Dennison in England. But these inventions seem to have been unknown to Wilsdorf and Ro-lex, and the screw down crown had to be invented again.

It is a principal of patent law that something that has already been in-vented cannot be patented—the prin-cipal of “Prior Art.” So the prior in-ventions should have prevented any-one from subsequently patenting the screw down crown. But as we shall see, Wilsdorf successfully obtained patents in Switzerland, Great Britain, the United States, France, and Germa-ny. How was this possible?

Although transatlantic patent trea-ties were in place at the time, means of communication and search were not so sophisticated as now, so the patent examiner did not realize that there was prior art. And patent offi ces do not guarantee patents. Once a pat-ent is published, it is up to the holder of a rival patent to challenge it. By the

time Wisldorf and Rolex got around to inventing the Rolex Oyster in the 1920s, over 40 years had passed since Fitch’s original patent, and it had not been taken up as an overwhelming commercial success.

The protection provided by the original patents had long since lapsed, and the inventors perhaps were re-tired or even dead, so there was no commercial interest to protect by challenging the Rolex patents, and it seems that the American designs had slipped into obscurity, if they were even known about on the opposite side of the Atlantic. Ultimately pat-ent law is based on litigation. If the holder of the priority patent does not choose to litigate, nothing happens, and the holder of the new patent may not even know of the prior patent’s existence.

The Rolex Oyster

Although the working environ-ment for a pocket watch may be

relatively benign, this is not the case for a wristwatch. In an exposed posi-tion at the end of its owner’s arm, it is vulnerable to the elements: to being knocked against things, plunged into water, and exposed to dusty condi-tions, so the need for robust move-ments and sealed cases to contain those movements is no longer an aca-demic exercise; it becomes an urgent necessity.

These considerations were not lost on Hans Wilsdorf, who was an early proponent of the wristwatch, placing a large order for “wristlet” watches with the Swiss fi rm of Herman Aegler virtually as soon as he had cofounded Wilsdorf and Davis in 1905, the fi rm that later became Rolex. Wilsdorf was well aware that one of the objec-tions to the wristwatch was its sus-ceptibility to dust and damp, which could rapidly spoil the mechanism. However, it appears that the earlier patents for screw down crowns were unknown to him when he set out to invent, or unknown to him, reinvent, the waterproof watch.

In the Rolex Jubilee Vade Mecum, the nearest thing we have to an of-fi cial history of the early days of Ro-lex, Wilsdorf wrote “To my technical



assistants, my constant refrain was, from the earliest days: We must suc-ceed in making a watch case so tight that our movements will be perma-nently guaranteed against damage caused by dust, perspiration, water, heat and cold. Only then will the per-fect accuracy of the Rolex watch be secured.”

By 1926 the Rolex technicians had achieved Wilsdorf’s goal and pro-duced the waterproof Rolex Oyster. But how exactly was this achieved? The description in the Vade Mecum is lacking in detail, to say the least, so unless we are to believe hearsay we must do some investigation. This leads me to the three patents men-tioned in the title of this article.

If you look in the case back of an early Rolex Oyster such as the one pictured in Figure 6, you will see four patents listed: British Patents 260554 and 274789 and Swiss patents 114948 and 120851. These are actually two pairs of patents, a British and a Swiss patent for each of two inventions. The fi rst British / Swiss pair (260554 / 114948) was for a waterproof screw down crown; the second pair (274789 / 120851) was for a waterproof case.

Investigating the fi rst pair reveals that the Swiss patent 114948 is the earlier and was registered by Paul Perregaux and Georges Perret of La Chaux-de-Fonds on October 30, 1925, and published on May 17, 1926. Figure 7 is an extract from the trade journal “La Federation Horlogere Suisse” dated 1st September 1926. This journal recorded the granting of watch-related patents, and also modifi cations to patents. In the

modifi cations section we can see the transfer of patent 114948 from Per-regaux and Perret to Hans Wilsdorf in July 1926.

But Wilsdorf was a shrewd busi-nessman and didn’t approach Per-regaux and Perret himself. Instead, he employed an agent, C. R. Spill-man et Cie SA of La Chaux-de-Fonds, to acquire the rights on his behalf, and then transfer them to him. The reason for this is most likely that if Perregaux and Perret realized that Wilsdorf, and thereby Rolex, wanted the rights to the patent, they would have been able to demand a higher price than they would have got from Spillman. The British version of this patent, 260554, was registered by Hans Wilsdorf, describing him-self as “Assignee of Paul Perregaux and Georges Perret,” on September 1, 1926, and published on April 21, 1927. Assuming that Wilsdorf hadn’t seen the Fitch, Twing, or Dennison patents, then this patent must have been the breakthrough that inspired Wilsdorf to create the waterproof

Rolex Oyster, so who were Paul Per-regaux and George Perret?

I have not been able to discover anything specifi c about Paul Per-regaux and Georges Perret. Jaquet and Chapuis2 mention a trade del-egation to Japan in the 1860s that included a Francois Perregaux of La Chaux-de-Fonds, who remained in Japan and imported Swiss watches. Pritchard3 lists Edouard Perregaux as a maker of pocket chronometers in Le Locle and Henri Perregaux as a maker of marine chronometers, also in Le Locle. Henri was father-in-law to Constant Girard, who appended his wife’s name on marriage as Gi-rard-Perregaux, and who of course is a famous watchmaker of La Chaux-de-Fonds. Pritchard also lists a Paul Perregaux of Neuchatel. None of these ties in exactly with a Paul Per-regaux of La Chaux-de-Fonds, but Le Locle, La Chaux-de-Fonds, and Neu-chatel are all within a few miles of each other, so this seems to show ev-idence of perhaps a family connec-tion between the name Perregaux

Figure 6. Oyster case back.

Figure 7. An extract from the trade journal “La Federation Horlogere Suisse.”

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and watchmaking in this area. Jaquet and Chapuis have nine en-

tries for Perrets involved in watch-making, and Pritchard has around twenty, all in the area of La Chaux-de-Fonds / Le Locle / Neuchatel. One of these, Paul Perret, is a very inter-esting character.

Paul Perret (1854-1903) of LaChaux-de-Fonds was an inventive horologist and watchmaker and an important character in the watch-making community of that town. He was awarded the very fi rst Swiss patent, CH 1, in 1888 for “Perfec-tionnements apportés à la construc-tion de mouvements de montres de toutes dimensions” (Improvements made to the construction of watch movements of all sizes) and went on to receive Swiss patents for at least 17 other inventions. These included new escapements and improvements in the compensation of balances. He worked with Charles Edouard Guil-laume, the inventor of Invar and Elinvar, on the application of those alloys to watch balances and was at the forefront of precision regulation of balances at the time. He is not the inventor we are looking for, but perhaps his inventiveness ran in the family and was inherited by a rela-tive or descendant.

Jules and Georges Perret of Epla-tures, near La Chaux-de-Fonds, today right on the very outskirts, received a patent in 1897 for a sim-plifi ed small seconds mechanism for Roskopf watches. Perhaps father and son, this Georges would seem to be a possibility for the co-patentee of CH 114948. Jaquet and Chapuis remark that the arrival of the railway led to an extraordinary expansion of La Chaux-de-Fonds, so that alongside Bienne and Geneva, it became one of the watchmaking capitals of the world. For someone from a small, less well-known town close to LaChaux-de-Fonds, it would be natural to give the larger town as their loca-tion.

From Jaquet and Chapuis and Pritchard we can see that there were numerous Perregauxs and Perrets working in the watchmaking indus-try in the area around La Chaux-de-Fonds, and very few with these

names anywhere else, so it seems likely that these were the names of two extended families. But who were Paul Perregaux and Georges Perret, and why did they work together on the patent? There are no other pat-ents in their joint names, so they don’t appear to have been at the forefront of watch technology devel-opment at the time, and patent CH 114948 seems to burst onto the scene like a bolt from the blue. Perhaps they were school friends in La Ch-aux-de-Fonds and developed the idea jointly, or maybe one or the other of these two gentlemen had been to America or Birmingham, England.

The two patents for the waterproof Oyster case, 120851 and 274789, were registered by Wilsdorf on September 21, 1926, and June 2, 1927, respec-tively. I only touch on the Oyster case design briefl y in this article, but I hope to revisit it at greater length in a subsequent article.

Returning to the evidence pre-sented in the Oyster case back in the form of the list of patents and their dates, we can infer that Paul Perregaux and Georges Perret in-vented the screw down waterproof crown, that Hans Wilsdorf of Rolex snapped up the rights to the inven-tion, a waterproof case was quickly designed, and the waterproof Rolex Oyster was born. From the way the patents are listed in the Oyster case

back, this appears to be what Rolex wanted people to believe, and this is the way James M. Dowling and Jef-frey P. Hess relate it in their book The Best of Time: Rolex Wristwatches4.

But I believe the true story is a little more complicated than this. The Per-regaux and Perret patent design has the same practical problems as the Fitch and Dennison designs, which I am fairly sure prevented Wilsdorf from ever putting it into production, and this leads me to my tale of the three patents.

The First Patent: CH 114948 —Perregaux and Perret

When Wilsdorf saw the Perregaux and Perret patent (Figure 8), he

must have thought he had found the solution he had been searching for to create a waterproof watch. He not only bought all rights to the Swiss patent and registered it as British patent 260554, he also registered it in Germany (443386) and the Unit-ed States (1661232). But I think he would have quickly realized that this patent wasn’t the complete answer. For the reasons why, let’s take a clos-er look at the Perregaux and Perret design.

The fi rst thing that struck me as odd about the Perregaux and Perret design is the shape of the crown. It is not like any early Oyster crown that

Figure 8. Perregaux and Perret Patent 114948.



I have seen. Figure 9 is a picture by Tommy Taylor showing three early Oyster crowns, the fi rst “onion” crown, the “small barrel” crown, and the later bubbleback crown. You can see how different they are to the Per-regaux and Perret crown.

The way the Perregaux and Perret design works is as follows: the wind-ing stem 4 and socket 6 are screwed together so that they are effectively one piece. The crown 8 is connected to the stem and socket assembly by two screws 9 and 10. The ends of these screws slide in the longitudinal slots 11 and 12 in Figure 8. This per-mits the crown to move axially with respect to the stem, as shown in the difference between fi gures 1 and 2 of the patent. But the screws ensure that the stem and socket are locked together rotationally. In this way Per-regaux and Perret allowed axial move-ment of the crown without requiring alteration of the keyless mechanism of the watch. As the crown is un-screwed from the case, the two screws slide up the longitudinal slots until the crown is clear of the pendant.

The screw thread on the pendant and the corresponding thread on the inside of the crown are left-handed. The reason for this is the same as in the Fitch and Dennison patents. When the watch needs winding, the crown is unscrewed clockwise, in the direction of winding. Once the watch is fully wound, and the hands set if required, then the crown is screwed back down anticlockwise, against the mainspring winding ratchet.

What isn’t stated in the patent is

how inconvenient the design would be to use in practice. As in the Fitch and Dennison patents, the reason for the left-hand thread is because once the watch is fully wound, the crown can no longer be turned fur-ther clockwise. The crown then must be screwed down in the direction al-lowed by the winding ratchet, which is counterclockwise or left-handed, the opposite direction to normal screw threads and therefore a rather unnatural action.

The use of a left-hand thread is a small drawback that wouldn’t have precluded use of the design in prac-tice, but there are also the same even more undesirable consequences to this design, as in the Fitch and Den-nison patents. Once the watch is fully wound and the crown screwed down, the crown cannot be unscrewed until the watch has run down somewhat, because the action of unscrewing the crown also winds the watch, and if the watch is already fully wound, it cannot be wound any more without breaking something. So if the hapless owner winds the watch fully, screws the crown down, and then realizes that the hands need setting, he is stuck for an hour or two!

The waterproof seal is also not ideal. It is formed by item 16, which is described as “a washer of elastic material impermeable to water.” As with Dennison’s patent, the principal problem with this would be fi nding a suitable material for the washer. The obvious materials available at the time, such as leather or cork, would not be very suitable for this applica-tion due to their tendency to com-press and harden with age and use. The exposed position of the washer at the base of the pendant on the outside of the case would also render it vulnerable to damage. With the crown being unscrewed every day to wind the watch, I wouldn’t expect this washer to remain effective for more than a month or two.

The Perregaux and Perret de-

signed screw down crown was less than ideal to say the least, with a less than ideal waterproof seal and requiring a good amount of educa-tion and subsequent care on the part of the customer if disaster was to be avoided. Wilsdorf must have realized that this design was not suitable to be released to the public. However, the idea of the screw down crown was there, and although as we have seen it was not an entirely new idea, it appears to have been new to Wilsdorf and the Rolex technicians, and provided the breakthrough that they were looking for.

There is a piece of clear evidence, provided by Wilsdorf himself, that Rolex didn’t actually use a left-hand-ed screw thread for the screw down crown of the Oyster. The second pair of patents listed in the Oyster case back, CH 120851 and GB 274789, are for the design of the waterproof Oys-ter case. A fi gure in these patents, re-produced as Figure 10, clearly shows that the thread on the case that the crown is to screw down upon, circled on the right in Figure 10, is clearly right-handed!

An interesting feature of the patent for the Oyster case is that it begins by saying that the invention refers to a shaped watch case (i.e., different from the usual round or circular form). The patent goes on to illustrate and describe an octagonal case as shown in Figure 10, and the means by which this case can be made watertight. This is why I chose to illustrate the opening of this article with the pic-

Figure 10. Oyster case patent.

An interesting aside is that a typing error has crept into the Dowling and Hess book. Georges Perret’s second name has been incorrectly spelled as

Peret. A Google search for “Rolex Perregaux Peret” reveals numerous plagia-rized copies of the Dowling and Hess text, complete with typo!

Figure 9. Early Oyster crowns.

PHOTO BY AND © TOMMY TAYLOR.



Figure 11. Patent CH 120848.

Square hole in base of cylinder 6

Square sectionon winding stem

Square hole in base of cylinder 6

ture (Figure 1) of the octagonal Ro-lex Oyster. But in fact the octagonal case shape is quite rare: most Oysters are either round or cushion shaped. I have a theory about why Wilsdorf chose to use an octagonal case form for the patent, but that will have to wait for my article about Oyster cas-es...

The Second Patent: CH 120848—Wilsdorf’sImproved Design

Wilsdorf’s imagination was evi-dently fi red up by the Per-

regaux and Perret design: a screw down crown was clearly the way to go. He put on his thinking cap, or more likely got his technical assis-tants at Rolex (Aegler) working on it, and by October 18, 1926, they had come up with an improved design. The patent for this was registered on October 18, 1926, as Swiss patent CH 120848 (Figure 11). Curiously, I have not been able to trace a British or any other version of this patent.

The clever bit of CH 120848 was that, as in Almon Twing’s design, a clutch was incorporated into the joint between the stem and the crown, so that the stem and crown would be coupled or decoupled depending on the axial position of the crown. This was a real breakthrough that over-came the problems of the Perregaux and Perret design. It meant that the crown could rotate freely while being screwed down and unscrewed from the case, but would become rotation-

ally locked to the winding stem when the crown was clear of the threaded pendant tube. The clutch also al-lowed the crown to be screwed down by a right-hand thread that would be familiar to any customer and meant that the crown could be safely un-screwed at any time to wind the watch or set the hands.

Referring to Figure 11 extracted from patent CH 120848, the opera-tion of the clutch, a dog clutch rather than a friction clutch, can be clearly seen. Cylinder 6 is screwed fi rmly into the crown so that they are locked together. The base of this cylinder has a square hole 9 in it. Plug 10 screws on to the end of the winding stem and has a circular fl ange 11 to center it within cylinder 6 and to support spring 13. It also has a square section 12 at its base, which corresponds with the square hole in cylinder 6.

When the crown is in its normal screwed down position as shown in fi gure 1 of the patent, there is no con-nection between the crown and the stem, and the crown is free to rotate in either direction (so far as allowed by the screw thread on the pendant) without turning the stem.

As the crown is unscrewed, it re-mains free to rotate relative to the stem until it is free of the screw threads, when it is pushed away from the pendant by the spring. As it is pushed away from the pendant, the square section 12 on the stem end plug drops into the square hole 9 in the base of cylinder 6, and the stem and crown are then locked togeth-

er rotationally. Cylinder 6 remains within the bore of the pendant and ensures that the crown remains co-axial with the pendant so that there is no danger of cross threading the crown on the pendant when it is screwed down.

When the crown is pushed back toward the case to screw it down af-ter winding the watch or setting the hands, the square section of the stem end plug pulls free of the square hole in the base of the cylinder, and the crown is then free again to rotate and be screwed down without turning the stem.

This design was the breakthrough needed to provide a practical, us-able, screw down crown for the wa-terproof Rolex Oyster, and it appears that Wilsdorf wasted no more time in putting the Oyster into production. Figure 12, again by Tommy Taylor, shows crowns from several early Oys-ters. The square dog clutch arrange-ment is clearly visible.

Where’s the Seal?

Before moving on from this pat-ent, we must ask where is the wa-

terproof seal? Strangely enough, this is not discussed in the patent, which merely states that when the crown is screwed down “all joints between the case, on the one hand, and the winding stem and crown, on the oth-er hand, are waterproof and prevent dust, moisture and water penetrating into the interior of the watch case.” (tous les joints existant entre la boite, d’une part, la tige de remontoir et la cou-ronne, d’autre part, sont etanches et em-pechent la poussiere, l’humidite et l’eau de penetrer dans l’interieur de la boite de montre.) As we noted in the case of the Fitch patent, a screw thread alone

PHOTO BY AND © TOMMY TAYLOR.

Figure 12. Early Oyster dog clutches.



does not form a watertight seal, so this description is rather lacking in detail, to say the least.

Although it is not described in the patent, inspection of the fi gures shows that the seal must be created where the base of cylinder, item 6, meets the end of the pendant, item 3. This would give a metal to metal joint, similar to the Fitch patent. If the base of the cylinder and the end of the pendant were well made, square, and fi nely fi nished, then a dusttight and watertight joint could have been achieved. It is not necessary to have a gasket to achieve a watertight joint, and in fact with the poor gasket ma-terials available at the time (e.g., as leather and cork), a metal to metal joint like this would have been a bet-ter option.

A Rolex brochure from the period says that “The famous Rolex Oyster is the original and only wrist watch that is permanently waterproof, dust-proof, perspiration proof without the use of any perishable materials whatever,” which confi rms that or-ganic gaskets such as cork or leather were not used. However, Tommy Taylor has informed me that early Oysters did use a lead gasket at this joint. Lead is not an ideal material for a gasket because it is not very elastic, and the role of a gasket is to accom-modate imperfect mating surfaces by deforming under compression to fi ll any small irregularities. But it is quite a soft metal, and so would have given some extra sealing to this joint whilst still preserving the metal to metal joint and avoiding the use perishable materials.

Early Oysters

You should note that the octago-nal Oyster case pictured in Figure

1 has lost its original onion crown, as have most early Oysters. It seems that there was a problem with either the stem or the stem receiver, the cylinder 6 in the patent, and that most Oysters have had their original crowns replaced by later versions. If anyone knows the full story of what happened, I would love to know.

Dowling and Hess report that they have seen Rolex Oysters bearing the

Glasgow Assay Offi ce import marks and the date stamp “d” for 1926, so clearly Rolex wasted no time in get-ting the watch into production once the technical diffi culties had been resolved. Aegler would certainly have produced prototypes in secret to prove the design before the patent was registered, and as soon as he had the protection of the patent, Wilsdorf would have ordered production to start.

The dating of these early Oysters to 1926 is not as certain as it seems at fi rst sight because before 1975 the Assay Offi ces did not change their year date letter on January 1, as might be expected. Before 1975 the London hallmarkiing year commenced on May 19, the Feast Day of Saint Dun-stan, patron saint of gold and silver-smiths, so an item marked with an “a” which Bradbury,5 the standard work on British hallmarks, says is the date letter for 1916, could have been marked at any time from May 19, 1916, to May 18, 1917.

The Glasgow year date letter was changed even later, but Bradbury is silent on this. Fortunately, Chaffer6

contains the vital information. The Glasgow year date letter was changed on July 1 every year. So Oysters marked with the Glasgow date letter ”d” would have been marked at the assay offi ce any time from July 1, 1926, to June 30, 1927. Notice I high-light the distinction between when they were marked at the assay offi ce

and when they were made, which is not recorded on the watches.

The Third Patent: CH 122110 —Weiss Drops A Bombshell

An interesting development to this story is that shortly after Wils-

dorf registered CH 120848, Philippe Weiss of La Chaux-de-Fonds patent-ed a similar design for a screw down crown in Swiss patent CH 122110. He also patented the same design in Brit-ain as patent GB 281315.

Weiss had hit on the same idea as Wilsdorf, to create a clutch between the crown and the stem. Wilsdorf’s patent CH 120848 was registered on October 18, 1926, and published in June 1927, beating Weiss to regis-tration by just over a month, Weiss registering CH 122110 on November 24. But it was a close run thing; I can imagine Wilsdorf having fi ts about what it would have cost him had Weiss got his patent registered fi rst!

Weiss’s invention is shown in Fig-ure 13, Weiss describes part of his in-vention as follows: “The winding stem is formed by two sections sliding one in the other, that is to say, on the one hand a rod 1 pivoted upon the plate, adapted to receive the winding pin-ion and the free pinion and to come into engagement with the bolt, and on the other hand a tube 2 screwed into the winding crown 3.” The tube 2 and the projections 12 on the rod form the clutch, in a similar manner,

Figure 13. Philippe Weiss Patent No. 122110.



but different form, to the square and square hole in Wilsdorf’s design.

But there is something that doesn’t look quite right about Weiss’s design. For one thing the wall thick-ness of the tube 2 circled in Figure 13 looks very thin. I scaled the draw-ing and, assuming that the crown is 5-mm diameter, the wall thickness of the tube along its thinnest part scales to 0.15 mm or about 6 thou-sandths of an inch. The projections on the winding stem would be a similar size.

Now I am not a watchsmith, but I am a professional engineer, and this seems very delicate to me. I would be concerned about the practicalities of making, assembling, and then hand-ing over to a customer, such a delicate object. And also how well it would wear in service. Remember that the practical automatic or self-winding watch won’t be invented for a few years yet, so the owners of these ear-liest waterproof watches would have to unscrew the crown and wind the watch every day, using the clutch each time.

I can’t see any particular reason why the tube and projections need to be this small, but this does indicate to me that the design hadn’t been prototyped, or actually made, before the fi gure in the patent was drawn, unlike the rather more practical and workman like design in Wilsdorf’s CH 120848 patent, and is therefore unlikely to have ever been manufac-tured.

But Weiss’s design was an alternative to Wilsdorf’s, and the patent contained a para-graph that must have come like a bombshell to Wilsdorf. “The invention is naturally not limited to the embodi-ment shown in the drawing. The two parts of the rod and their co-operating driving members may be entirely different.”

This was a broader claim than contained in Wils-dorf’s CH 120848 patent, which is quite tightly writ-ten around the particular embodiment of dog clutch described above. It is almost

as if having invented the specifi c de-sign described in the patent, with the square section on the winding stem engaging with the square hole in the base of the cylinder, Wilsdorf and his technical assistants couldn’t imagine that anyone would think of another way of coupling and decoupling the winding stem and crown, so they didn’t think to write up the patent in a more general way.

But Weiss had come up with an al-ternative design. Although Wilsdorf’s patent was registered fi rst, and would therefore take precedence, with his broad claim Weiss had shut off to Wilsdorf any design that wasn’t al-ready in Wilsdorf’s tightly written patent description. This could hamper any future developments or improve-ments of the Wilsdorf design, because Weiss could potentially sue for patent infringement. Wilsdorf must have re-alized that he had to secure the rights to Weiss’s patent as well!

Wilsdorf’s patent CH 120848 was published on June 16, 1927, less than eight months after registration, but Weiss’s patent was not published until December 16, 1927, nearly 13 months after registration. I wonder if the delay in publication of Weiss’s patent was because he knew Wilsdorf got there fi rst—perhaps because he was already in negotiation with Wils-dorf. In fact, in view of the obvious overlap between the two designs, it would be surprising if the patent au-thorities had allowed Weiss’s patent

to go through, unless perhaps Wils-dorf had already purchased the rights so there was no confl ict of interest.

There is some circumstantial evi-dence that Wilsdorf acquired Weiss’s patent rights because another Weiss patent, CH 130195, was registered on November 30, 1927, in Switzerland by Wilsdorf. This was before Weiss’s patent 122110 was published. This patent doesn’t mention Weiss by name, but although it was registered by Wilsdorf, we know that it was a Weiss patent because the same de-sign was also registered in the United Kingdom by Wilsdorf as assignee of Philippe Weiss, patent number GB 303102 on September 25, 1928.

There is also a piece of conclusive evidence that Wilsdorf purchased the rights to Weiss’s patents. This comes in the form of a Rolex advertisement from October 1929 issue of The Practi-cal Watch & Clock Maker, shown in Fig-ure 13. In small print are listed three patents, 260559, 274789, and 281315. The fi rst of these is a mistake, correct-ed in later ads; it should read 260554, the U.K. version of the Perregaux and Perret patent. The second, 274789, is the UK version of the Oyster case pat-ent. And the third, 281315, is the U.K. version of Weiss’s patent screw down crown, showing that Weiss’s patent was fi rmly under Rolex ownership.

Concluding Remarks

That concludes my story of the development of the

screw down crown. It is inter-esting that the inventions of Fitch and Twing in America in 1881 had all of the char-acteristics required for a suc-cessful waterproof crown, yet they were not a commercial success. I believe that this was because the additional complication was not widely regarded as necessary on a pocket watch and, if Wilsdorf and Rolex are to be believed (and I have no reason to doubt them) these pioneering inventions were unknown or forgotten in Europe 30 or 40 years later, when the fashion for strapping a watch to one’s Figure 14. 1929 Rolex advertisement.



wrist made the need for better seal-ing to protect the movement a neces-sity. It also concludes my tale of the three Rolex patents: the Perregaux and Perret patent that was probably never built, but widely referenced by Rolex in the early Oyster case backs; the improved Wilsdorf patent that was actually used in the early Oys-ters but only registered in Switzer-land; and the Weiss patent, which must have made Wilsdorf curse that his patent was so tightly defi ned and forced him to buy the rights to keep open potential future developments. There were other designs and patents of course, but I believe these three were the ones most critical to the de-velopment of the screw down water-proof crown of the Rolex Oyster.

There are of course still many un-answered questions, such as why CH 120848 was only ever registered in Switzerland, unlike the Perregaux and Perret patent, which was reg-istered in many counties, and why Wilsdorf and Rolex continued to re-fer to the Perregaux and Perret patent in the case backs of Oyster watches, even though the screw down crown actually used was of a very different design. And were any watches ever constructed to the Perregaux and Per-ret patent design, even as prototypes, with left-hand threaded crowns and pendants?

I have a feeling that this is not the end of the story. And as I mentioned earlier, there is still the design of the Oyster case to examine ... D

Acknowledgments I thank Crispin and Sam at www.

oldetimers.com for information based on their stock of early Rolex Oysters and for the use of the pic-tures of the early Rolex Oysters; Tommy Taylor for information on the construction details of early Oysters and the pictures of the early Oyster crowns; Tom McIntyre for reviewing the article and informa-tion about the American Watch Co. and Waltham watches; Jerry Treiman for the picture of the pocket watch with the screw down crown; and Jake Ehrlich of Jake’s Rolex World Magazinefor the picture of the ad from The Practical Watch & Clock Maker. I also

thank everyone from the NAWCC and TimeZone forums who have an-swered my questions while research-ing this article.

Any mistakes, errors, and omis-sions are entirely my own, and I would gratefully receive any correc-tions and additional information.

References 1. Rolex Jubilee Vade Mecum

(Geneva: Rolex Watch Co.Ltd., 1946).

2. Eugene Jaquet and Alfred Chapuis, Technique and History of the Swiss Watch (Germany: Graf Verlag, 1953).

3. Kathleen H. Pritchard, Swiss Timepiece Makers 1775-1975 (West Ken-nebunk: Phoenix Publishing, 1998).

4. James M. Dowling and Jeffrey P. Hess, The Best of Time Rolex Wristwatch-es: An Unauthorized History, 2nd edition (London: Schiffer, 2001).

5. Frederick Bradbury, Bradbury’s Book Of Hallmarks (Sheffi eld Assay Of-fi ce, revised ed., 2002).

6. C.A. Marlhams, Chaffer’s Hand-

book To Hallmarks On Gold & Silver Plate, 6th edition (London: W. Reeves, 1936).

About the Author David Boettcher lives in Cheshire,

England. He worked for 20 years in the nuclear power construction in-dustry in the UK before leaving to work for himself. He holds a degree in Engineering Science from the University of Bath, is a Chartered En-gineer, a member of the Institute of Engineering and Technology and a registered European Engineer. He has pursued careers in retail and IT, and now works as a freelance Engineer, IT consultant, and web designer. His interest in vintage wristwatches was sparked when he inherited his grandfather’s 1918 silver Rolex and grandmother’s 1917 gold Rolex wrist-watches. His web site is www.Vintage-WatchStraps.com and he can be con-tacted by email at [email protected].

Number Title Inventor Published

US 237,377 Stem-Winding Watch Key

Ezra C. Fitch February 8, 1881

US 243,011 Stem winding and setting device for watches

Almon Twing June 14, 1881

GB 1390 Improvements in or con-nected with watches

Gilbert Dennison October 21, 1915

CH 114948 Montre a Remontoire Paul Perregaux & Georges Perret

May 17, 1926

GB 260,554 Improvements in keyless watches

Hans Wilsdorf, Assignee of Paul Perregaux and Georges Perret

April 21, 1927

CH 120851 Boite de montrede forme

Hans Wilsdorf June 1927

GB 274,789 Improvements in or relating to watch cases

Hans Wilsdorf July 28, 1927

CH 122110 Montre hermetique a remontoir

Philippe Weiss December 16, 1927

GB 281,315 A Fluid-tight Keyless Watch

Philippe Weiss March 29, 1928

GB 303,102 Fluid-tight Keyless Watch Hans Wilsdorf, Assignee of Philippe Weiss

July 4, 1929

List of Patents Mentioned in Order of Date of Publication


rolex screw down crown - welcome to the nawcc! · n 1926 rolex created the waterproof rolex oyster...

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