the fundamental problem in thread gaging and thread gage ... · thread set plugs and thread ring...
TRANSCRIPT
NCSL International Workshop & Symposium | Measurements of Tomorrow August 27-30, 2018 | Portland, Oregon
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The Fundamental Problem in Thread Gaging and Thread Gage Measurement
Speaker/Author: Travis Fletcher
Quality Engineer / Process Engineer
JJ Calibrations, Operations Manager
Portland, OR 97267-2105
503-786-3005
Since the introduction of threads and thread specifications measurement practices have made
assumptions based of formulas and calculations. While this has allowed for what has been deemed as
adequate measurement of threaded parts and gages technological advances have brought to light some
fundamental issues.
For the sake of this evaluation, we will be focusing only on 60° Unified Screw threads. Specifications
for these types of screw thread parts can be found in ANSI /ASME B1.1 (Unified Screw Threads) and
ANSI / ASME B1.2 (Gages and Gaging for Unified Inch Screw Thread Series).
To ensure that threaded products produced meet specifications, Go / NoGo thread plugs and thread
rings are typically used. In theory, this is pretty simple; The Go Gage must pass the threaded section of
the part and the NoGo gage must NOT pass.
Inspection of Internally Threaded Parts
Inspection of internal threads has traditionally been with the use of thread plug gages. Parameters for
inspection of these types of internal threads are typically simplified to two main requirements; Pitch
Diameter (PD) and Minor Diameter. The Go Gage is designed to encompass the low end of the
specification for the PD (with + tolerance applied) and the major diameter to account for the nominal
size of the thread size designation (with + tolerance applied). The NoGo Gage is designed to
encompass the high end of the specification for the PD (with - tolerance applied) and the major
diameter to account for the nominal size of the thread size designation (with - tolerance applied). Pretty
simple, right? So, how are these gages that are manufactured to inspect threaded parts being
manufactured being inspected? Please, read on...
Inspection of Externally Threaded Parts
Inspection of external threads has traditional been with the use of thread ring gages. Again, parameters
for inspection of these types of internal threads are typically simplified to two main requirements; Pitch
Diameter (PD) and Major Diameter. The Go Gage is designed to encompass the high end of the
specification for the PD (with - tolerance applied) and the major diameter to account for the nominal
size of the thread size designation (with - tolerance applied). The NoGo Gage is designed to encompass
the low end of the specification for the PD (with + tolerance applied) and the major diameter to account
for the nominal size of the thread size designation (with + tolerance applied). So, again, how are these
gages that are manufactured to inspect threaded parts being manufactured being inspected? Please read
further on for explanations, but first we need to also discuss other facets of the inspection of externally
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threaded parts that should mentioned. On External Threads, the PD's and major diameters are typically
also verified using other methods as well. I have come to the conclusion that while this is a great
practice the only reason this is done on external threads and and not on internal threads is because it
CAN be done without having to destroy a sample part to obtain measurements by sectioning it. Major
Diameters are typically measured using an OD micrometer. PD's are often measured using a thread
pitch micrometer, a Johnson Gage roll comparator, or with and OD micrometer, using the 3-wire
method. For the sake of this evaluation, we will only be focusing on measurements with an OD
Micrometer, with adequate resolution / accuracy for these tight tolerances; I.E. and indicating
micrometer or “supermic.” (Feel free to contact me if you want additional information on the other
methods mentioned).
Measuring of Pitch Diameters using a Supermic and the 3-Wire Method
The 3-Wire Method can be used to measure externally threaded parts, thread plug gages (used for
inspecting internally threaded parts), and thread set plugs (used for inspecting and setting thread ring
gages that are in turn used to inspect externally threaded parts). Before we get much further into
measuring using the 3-Wire Method, we first need to understand what the Pitch Diameter (PD) is.
So, what is a pitch diameter of a screw thread? The best definition that I have run across is as follows:
The diameter of a theoretical cylinder that passes through the threads in such a way that the distance
between the theoretic sharp corner of thread crests and the theoretic sharp corner of the thread roots is
equal. So, how do we measure the theoretic points of features that create a theoretical cylinder? To put
it simply, the only way is to do it “theoretically”, making some assumptions and performing
calculations using mathematical formulas for constants. Huh? Basically, you cannot measure to and
from surfaces that do not physically exist. So, how are measurements actually obtained? PD
measurements can be performed by using the 3-Wire Method to simulate measuring the actual PD. For
example, on a 1/4-20 UNC-2B thread plug gage, a wire size is determined using the following formula
(applies to all 60° Unified Inch Screw Threads):
.57735 / Threads Per Inch (TPI) = Best Wire Size
.505182 / TPI = Min Wire Size
1.010363 / TPI = Max Wire Size
With a TPI of 20, the Best Wire Size is calculated as .0288675 (rounded up to .028868)
With a TPI of 20, the Min Wire Size is calculated as .0252591 (rounded down to .025259)
With a TPI of 20, the Max Wire Size is calculated as .05051815 (rounded down to .050518)
If these exact wire sizes are not available, as long as the 3 available wires are the same size (within
specifications for thread measuring wires) and within the min / max wire sizes allowed, we can still use
the wires to obtain measurement results by applying the following formula:
C=3W- (.866025p)
Where
C = Constant to be used in 3-wire method
W = Mean (average) of thread wires
p = pitch
Given our example of 1/4-20 threads, let’s say only three .0300” wires were available for use. We can
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use these wires by calculating the following:
(Thread wires are theoretically the same exact size for this example)
TPI = 20 or .050 pitch (1 inch divided by 20 Threads Per Inch)
p = .050
W = .0300”
3x.0300 = .09
.866025 x .05 = .04330125
.09-.04330125 = .04669875 Rounded to 6 decimals = .046699 (Constant)
The constant is the numerical value that is subtracted from the measurement over the wires placed in
threads of the unit under test (the part or gage to be measured).
Thread wires should be placed in the threads of the unit under test as shown below:
Measurements over wires obtained should have the constant subtracted from the measurement result to
obtain the calculated Pitch Diameter. Measurement Over Wires (M.O.W.) - Constant ( C ) = PD
Unfortunately, and as previously mentioned, this is a theoretical calculation of the pitch diameter using
mathematical formulas and may not capture the actual pitch diameter. What this method captures is
what is known as the “simple pitch diameter.” So, how do we measure the actual effective Pitch
Diameter? Up until only the past couple of years, there really wasn't a way to legitimately measure the
actual Pitch Diameter. Now, with improvements in Technology, there is by scanning the profile of the
threads using a contact scanning measurement device.
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Why Contact Profile Scanning?
Contact profile scanning allows for actual contact measurement of the critical features of the thread that
constitute the true effective pitch diameter. This method is already widely practiced in most parts of
Asia. In Europe, the method has become the standard from which most thread measurements are
derived (ref Euramet cg-10). This method removes several of the variables that occur during the 3-wire
method for pitch diameter measurement while also capturing the entire profile of the thread instead of
just a small section that the wires come into contact with along the thread flanks. Additionally, this
method removes the potential for tolerance stack-up by relying on the accuracy of the scanning device
and probe rather than the accuracy of each of the 3 wires and the super micrometer while
simultaneously reducing the variation of measurement result by different inspectors.
Thread Set Plugs and Thread Ring Gages
As previously mentioned, inspection of external threads has traditionally been with the use of thread
ring gages. To ensure that threaded products produced meet specifications, Go / NoGo thread rings are
typically used. The Go Gage must pass over the threaded section of the part and the NoGo gage must
NOT pass. So, how are these thread ring gages that are being manufactured being inspected to ensure
that they meet specifications? Up until recent technological advances, thread set plugs have been used
for this purpose. Thread Ring Gages are threaded onto a thread set plug to ensure proper feel on both
the truncated portion and full form portion of the thread set plug. Proper feel has been defined as
“Some Drag” or “Slight Drag.” What could be clearer than that, right? Being more of a data-driven
person, this is extremely subjective in my opinion and I have seen countless man-hours spent on this
discussion. What may feel like “some drag” or “slight drag” to Inspector A may be drastically different
from what Inspector B feels as the correct fit. This being said, there is a little more to it than just “some
/ slight drag.” In addition to the thread ring gage being threaded onto both the truncated and full form
of the thread set plug with slight drag, there should also be no difference in feel between the truncated
and full form sections. There should also be no “wobble” detected while threading the ring onto the
thread set plug. There should also be no difference in feel or any wobble detected when the gage is
flipped over and ran onto the set plug from the opposite side. Again, these requirements are subjective
and open to interpretation and may be the subject of lengthy discussions between operators, QA
personnel, calibration technicians, etc. So, what does it mean if the drag is not tight enough? What does
it mean if the drag is too tight? What does it mean if there is a difference in feel between the truncated
and full form sections of the thread set plug? What does it mean if there is wobble? What does it mean
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if one side of the gage feels correct, but when it is flipped over and ran onto the set plug from the
opposite side it feels different, has wobble, is too loose or too tight? Let me explain:
On fixed (non-adjustable) thread ring gages, the ring should be replaced if:
Drag is excessive and the ring does not turn adequately (without significant force) on either the
truncated section or full form section of the thread set plug.
There is not enough drag on either the truncated section or full form section of the thread set
plug and the ring is “free-spinning.”
The ring gage exhibits wobble or excessive slop when run onto either the truncated or full form
section of the thread set plug.
One side of the ring threads onto the thread set plug, but when turned over and threaded on
from the opposite direction, there is excessive drag, not enough drag (free-spinning), or wobble.
On adjustable thread ring gages:
If drag is excessive and the ring does not turn adequately (without significant force) on the
truncated section of the thread set plug, it will need to be adjusted (loosened) to fit the truncated
portion of the thread set plug.
If there is not enough drag on the truncated section of the the thread set plug and the ring is
“free-spinning”, it will need to be adjusted (tightened) to fit the truncated portion of the thread
set plug appropriately.
If drag is excessive and the ring does not turn adequately (without significant force) on the full
form section of the thread set plug, but it threads on to the truncated section correctly, the gage
may be able to be adjusted, however, this is somewhat difficult. Consider replacing the gage, as
the flanks may be worn.
If there is not enough drag on the full form section of the the thread set plug and the ring is
“free-spinning”, but threads on to the truncated section correctly, the gage may be able to be
adjusted, however, this is somewhat difficult. Consider replacing the gage, as the flanks may be
worn.
Potential for Tolerance Stack-up & TAR with the 3-Wire Method
Now that we understand the interaction between the thread set plug and the thread ring gage, lets re-
visit the 3-wire method of inspection for PD's on thread set plugs. Going back to our example of 1/4-20
threads, the tolerances for thread measuring wires, thread set plugs, and thread ring gages are shown
below:
Thread Measuring Wires:
±.000020” of best wire size
±.000005” of specified wire size
±.000005” of each 3 wires to each other
±.000010” roundness
1/4-20 UNC-2A thread set plug (Go member used for example)
.2164” +0 / -.0002” Pitch Diameter
.2489” ±.0004” Major Full Form Diameter
.2399” +0 / -.0004” Major Truncated Diameter
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1/4-20 UNC-2A thread ring (Go member used for example)
.2164” +0 / -.0003” Pitch Diameter
.1948” +0 / -.0005” Minor Diameter
For arguments sake, lets assume conditions where ALL measurements were at the absolute minimum to
still be considered acceptable;
Thread measuring wire:
Best Wire Size .028868 -.000020 = .028848
Specified wire size .028848 -.000005 = .028843
High wires = .028843
Low wire = .028843-.00005 = .028838
Out of round condition min = .028837
Out of round max = .028844
In actuality, the wires specified as .028843 can measure as much as .028844 and as low as .028837
depending on where the measurements are taken. How does this effect measurements on the thread set
plug? A .000007” difference in thread wires wouldn't effect a measurement on a thread set plug, right?
Not exactly, if not accounted for correctly, with a new constant calculated, a .000007” difference in
thread wires could change the constant by .000021”. With the constant being the number that is
subtracted from the measurement over wires (M.O.W.) to obtain the calculated, simple pitch diameter,
this could drastically impact measurement results. With this value in addition to typical accuracy of a
super micrometer of ±.000020”, measurements of calculated pitch diameter could be off by as much as
.000041”, or over 20% of the allowable tolerance of the thread set plug. While this is acceptable as it
meets a 4:1 Test Accuracy Ratio (T.A.R.), consider the following;
At a measured PD of .2164” (max PD for 1/4-20 UNC-2A thread set plug) the unit under test could
actually measure .216441”.
At a measured PD of .2162” (min PD for 1/4-20 UNC-2A thread set plug) the unit under test could
actually measure .216159”.
Set Plugs and Thread Ring Gage Tolerances Compared to Manufactured Nut / Bolt
Specifications
Going back to our example of 1/4-20 threads, the tolerance for thread set plugs, and thread ring gages
are shown below:
1/4-20 UNC-2A thread set plug (Go member used for example)
.2164” +0 / -.0002” Pitch Diameter
.2489” ±.0004” Major Full Form Diameter
.2399” +0 / -.0004” Major Truncated Diameter
1/4-20 UNC-2A thread ring (Go member used for example)
.2164” +0 / -.0003” Pitch Diameter
.1948” +0 / -.0005” Minor Diameter
Do the gages manufactured actually meet these specifications?
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In reviewing thread ring gages specifications, once again using our example of 1/4-20 UNC-2A, the
pitch diameter requirements for the GO ring is listed as .2164” +0 /-.0003”, or .2164”-.2161”. The
correlating thread set plug GO member requirements for pitch diameter is listed as .2164” +0/-.0002”,
or .2164-.2162”.
Generally speaking, NO, the adjustable thread ring gages manufactured to meet these specifications do
NOT meet the defined dimensional tolerance. Here is my theory as to why;
Let’s go back to our definition of the pitch diameter: The diameter of a theoretical cylinder that passes
through the threads in such a way that the distance between the theoretic sharp corner of thread crests
and the theoretic sharp corner of the thread roots is equal.
If the diameter of a shaft made of steel and the diameter of a hole machined out of steel are the same
size, will the shaft enter the hole with “slight drag”? No, the shaft would have to be slightly smaller to
enter the hole or use significant force to be driven into the hole. Even though the the pitch diameter is a
theoretical cylinder, it is still based off of the flank angles of the thread. Knowing that thread ring gages
and thread set plugs are manufactured from steel (sometimes chrome), it is not possible for a steel shaft
(I.E. the set plug) to enter the hole machined from steel (I.E. the thread ring gage) without significant
force being applied. In reference to ANSI B4.1 for Standard Tolerance Limits and Fits, there are 3 main
classes of fit: Running or Sliding Fits [RC], Locational Fits [LC, LT, LN], and Force or Shrink Fits
[FN]. The Locational Fit class can be broken down into 3 sub-classes; Clearance Locational Fit [LC],
Transition Locational Fits [LT], and Interference Locational Fits [LN]. While this specification applies
to non-threaded cylindrical features, I believe a little can be learned from this standard in regards to
the fit of a thread ring gage onto a thread set plug.
Revisiting our use of the thread set plug and proper testing of the thread ring gage:
Thread Ring Gages are threaded onto a thread set plug to ensure proper feel on both the truncated
portion and full form portion of the thread set plug. Proper feel has been defined as “Some Drag” or
“Slight Drag.”
The “Slight Drag” description would best fit the Running or Sliding Fit classification of RC2 in ANSI
B4.1; Intended for accurate location made to move and turn easily but not freely. I believe this can
further be substantiated by matching the tolerance band of the PD for the 1/4-20 UNC-2A thread ring
gage of .2164”-.2161” to hole requirements for this class of .2164-.2161” when the nominal size is
specified at .2161”. However, when compared to the shaft requirement of .21595-.21575” for this class
of fit compared to the set plug requirements of the 1/4-20 UNC-2A thread set plug of .2164-.2162” we
see a problem. ANSI B4.1 knows that for this class of fit, the shaft (set plug in example) must be
slightly smaller than the hole (ring gage in example). To get even remotely close to the matching the
dimensional requirements of the 1/4-20 UNC-2A thread ring gage and thread set plug, we have to look
not one or two classes of fit beyond RC2, but rather 9 classes to class LN 1 (Locational Interference
fit), with a hole requirement of .2164-.2161” compared to a shaft requirement of .2166-.2164”.
“Slight Drag” of the thread ring gage cannot be achieved by threading it onto the thread set plug with
the amount of force required if both the thread set plug and the thread ring gage met the dimensional
limits of the specifications.
It is obvious that the writers of thread specifications know this, as when we review the specifications
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for externally threaded parts / screws / bolts and internally threaded parts / nuts we see that the Pitch
Diameters of the mating parts do NOT overlap:
Pitch Diameter for Externally threaded parts / screws / bolts for 1/4-20 UNC-2A thread requirement is:
.2164-.2127”
Pitch Diameter for Internally threaded parts / nuts for 1/4-20 UNC-2B thread requirement is:
.2224-.2175”
In other words, the theoretical cylinder of the pitch diameter of the shaft (screw / bolt) CANNOT be the
same size as the pitch diameter of the hole (nut) to function correctly. The shaft (screw / bolt) must be
at least .0011” smaller than the hole (nut). This of course, would be a looser class of fit, though, as we
don't want our threaded parts having “slight drag” as we want our rings to thread onto our set plugs.
This is why min / max sizes of threaded parts allow for a fit that can accommodate a simple, turn by
hand and / or screw driver (similar to ANSI B4.1 RC9 for loose running fits with a hole requirement of
.2220-.2190” compared to a shaft requirement of .2145-.2130” when the nominal size is specified at
.2190”. )
Additionally, it needs to be considered that whenever the adjustable thread ring gage is adjusted, it
applies stress to the adjustment point of the gage being adjusted. Instead of being cylindrical in nature,
the adjustment process forces the gage into being more triangular. While the intent of the relief holes /
cut-outs is to address this issue, the results of the dimensional studies performed show that they are not
fully effective.
The fundamental problem is that adjustable thread ring gages set to thread set plugs, in all likelihood,
DO NOT meet the dimensional tolerance limits of their applicable specifications.
As I mentioned, this is my theory. Like all theories, they require proof before they become fact. I'd like
to share with you at this time the proof that supports this theory:
1A study of 30 adjustable thread ring gages was performed using the Master Scanner to obtain
measurements of pitch diameter and minor diameter. Of these 30 adjustable thread ring gages, not a
single gage was found to meet both tolerance for pitch diameter and minor diameter. Gages used for
this study were all 60° Unified Screw threads and encompassed a range of TPI's, classes of fits, and
nominal sizes. Out of the 30 adjustable thread ring gages, only one gage was found to have a pitch
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diameter within dimensional limits (approx. 97% failure rate), however, the minor diameter was found
out of tolerance, so it could not be considered as meeting specifications. Out of the 30 adjustable thread
ring gages, only 10 were found to have minor diameters within dimensional limits (approx. 67% failure
rate), however the pitch diameters were out of tolerance, so these gages could not be considered as
meeting specifications. This study showed that 100% of the thread ring gages analyzed failed to meet
specifications. Measurement results are shown below, as deviation from nominal):
1
1A 2nd
study was performed where an adjustable thread ring gage was properly set to the correlating
thread set plug and then measured at various points around the perimeter of the diameter. Again, this
ring was found out of tolerance for all pitch diameter measurements, regardless of where the
measurement was taken. The interesting thing about this particular study was the interaction between
the pitch diameter readings and the minor diameter readings. Where the PD's were found larger, the
minor diameters were found smaller. Results are charted results below:
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1A 3rd
study was performed using this same adjustable ring gage where it was continuously adjusted
until it the Pitch Diameters and and Minor Diameters were brought as close as possible to reading
within tolerance, as unfortunately both could not be adjusted in. The closer the PD's were brought into
meeting tolerace, the tighter the ring was to the set plug. At the point where both the PD's and Minor
Diameters were adjusted into being as close as possible to the defined dimensional requirements, the
ring was so tight on the thread set plug it took as much as 55 in/lbs of force to be applied to thread onto
the set plug with mechanical assistance. This, of course, does NOT meet the requirements of “slight
drag.” (This can also further substantiate the comparison to the ANSI B4.1 LN 1, Locational
Interference fit mentioned earlier.) When this thread ring was correctly set to the correlating thread set
plug only 2-5 in/lbs of force was required to achieve the “slight drag” requirements.
Conclusion and Next Steps
So what does all this mean? I suppose it all depends on what your role is in regards to threads, thread
gaging, and thread specifications. Does this mean that all adjustable thread ring gages are “bad”? I
try to avoid the word “bad” when evaluating for conformance to specifications. I prefer the terms
“within tolerance / out of tolerance” and / or “meets specifications / does not meet specifications.”
Adjustable thread ring gages can still be used and are a good tool for evaluating thread functionality,
however, they most likely will NOT meet the dimensional specification requirements. Please see the
following pages for recommendations.
For the manufacturer using thread gages to inspect thread products you are producing:
If you need to ensure that your thread products not only work properly, but also need to ensure
that the product meets specification requirements, be knowledgeable of thread specifications
and specifications of the gages being used. Ensure that your gages are calibrated and adequate
for the jobs you are running. The author not only recommends inspecting externally threaded
parts with fixed (IE non-adjustable) thread ring gages, but also verifying parts produced for
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major diameter with a micrometer and pitch diameter with a johnson gage roll comparator or by
using the 3-wire method with a super micrometer, if a Contact Scanner cannot be purchased. If
you are using adjustable thread ring gages to inspect threaded parts produced it is absolutely
critical that you inspect the major diameter and pitch diameter as described above. It is also
critical that you also own the correlating thread set plug so that the adjustable thread ring gages
can be set correctly and periodically evaluated to ensure they are acceptable for use. The thread
set plug should be sent in to a calibration laboratory for periodic calibration. If you feel
confident setting and adjusting the thread ring gages yourself you may choose to perform this
action yourself, rather than sending the ring gage in for calibration. If you do not feel confident
in setting and adjusting thread rings gages, they should be sent into a calibration laboratory for
service at the same time as the correlating thread set plug. If your company owns an adjustable
thread ring gage, it is absolutely critical that you also own the correlating thread set plug. Due
to the shear number of different thread sizes, pitches, classes of fit, configurations, and custom
pitch diameters available it is absolutely impossible for a single calibration laboratory to own
every possible correlating thread set plug. Adjustable thread ring gages can also be calibrated
using a contact scanner (if your calibration provider has one available for use), however, as
shown they will most likely be found out of tolerance using this method.
It also needs to be strongly re-iterated that simply using Go / NoGo Thread Ring Gages is not
an adequate way to determine the acceptability of manufactured externally threaded
components. This is true regardless of whether the rings are fixed or adjustable. Go / NoGo
Thread Ring Gages should be used as more of a functionality check and other methods, as
previously mentioned, need to be employed to determine acceptability to specification
requirements.
For the calibration laboratories calibrating thread ring gages:
The author recommends utilizing the Contact Scanning method for calibration. If a Contact
Scanner is used, report your measured values and if they are out of tolerance to specifications,
list them as such. It does no good to the user of these thread ring gages to just know reported
actual values. They need to know if the thread ring gage they have purchased and are using
meets specifications. Additionally, if enough thread ring gages are found to be out of tolerance,
this will bring further attention to this issue and it will need to be addressed by the
manufacturers and the ASNI/ ASME advisory boards. This will, hopefully, drive changes to
specifications and / or methods to which these units are produced and inspected.
If a Contact Scanner cannot be purchased for use, a thread set plug must be used for calibration.
Since this is a tactile calibration, it is strongly recommended it is listed as such on the
calibration certificate. It is also recommended that any numeric measurement results reported
are clearly defined as having been obtained from the thread set plug and not the thread ring
gage itself.
For the manufacturer producing thread gaging products:
The author strongly recommends purchase of a contact scanner to measure thread plugs, set
plug, and ring gages to ensure that they meet specifications. It is also recommend to only offer
fixed ring gages, as they have proven more reliable in meeting dimensional requirements. If
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neither of these are options for your company it is absolutely imperative that the method of
inspection and qualification of the adjustable thread ring gage is clearly defined. It is also
strongly recommended that a correlating master thread set plug is offered at the time of
purchase of adjustable thread ring gages and they are ONLY sold as sets.
For the members of the ANSI / ASME advisory boards for thread specifications:
With this information being presented and further studies in process, specifications on thread
ring gages absolutely need to be reviewed and reconsidered. It is pointless to have
specifications that cannot be achieved. It is the authors recommendation that this issue can be
addressed by one or more of the following approaches:
o Adjustable thread ring gages specifications be revised to allow for achievable
dimensions that will still work for allowing only acceptable products or to list the Pitch
Diameters and Minor Diameter requirements as reference only dimensions with no
tolerance applied.
o Adjustable thread rings gages have the current specification applied to them for the
purpose of the manufacture of these gages only. The manufacturer would then be
required to list the measurement results utilizing a Contact Scanner. After initial
manufacture and first article inspection of each and every gage produced, subsequent
inspections, setting, and or adjustment would need to be done using the correlating
thread set plug. It would need to be a requirement that thread set plugs are supplied at
the time of purchase of the adjustable thread ring gage and that adjustable thread ring
gages are only sold as a set with the correlating set plug.
o Adjustable thread ring gages are designated as obsolete and fixed thread ring gages take
their place.
References
ANSI / ASME B1.1 Unified Inch Screw Threads
ANSI / ASME B1.2 Gages and Gaging for Unified Inch Screw Thread Series
Euramet cg-1 Determination of Pitch Diameter of Parellel Thread Gauges by Mechanical
Probing
ANSI / ASME B4.1 Preferred Limits and Fits for Cylindrical Parts