woodscrew specifications - autonopedia

11/10/11 Woodscrew Specifications - Autonopedia

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Woodscrew Specifications

Here you may select the appropriate screw for your project. Some of those pesky technical descriptions arenecessary: The terms "phillips", "square drive", "slotted", and "truss head", refer to the kind of driver used toturn the screw.The shape of the screw head is described as "flat", "oval", "round", "truss", "bugle", or"hammered". Looking at the drawings should make these self-explanatory.

The general size of a screw is given a number. As the number increases, so does the size of the entire screw,both head size and shaft size--but not length.Therefore, a #8 screw is about twice the size of a #4 screw, butmay be the same length. This is important. Most wood screws have a common "pitch" to the threads, but somehave a thread with a steeper incline. This is called a "fast" thread. Think of this as a road going up a mountain;the steeper the road, the sooner you get to the top.

Also in reference to threads you will see "8-32". This is the common knob and pull screw thread. The"8" refersto the size (diameter) of the screw, and the "32" means it has 32 threads to the inch. And then, the are thosetermed "various finishes". Check them out and select the right one to match you project.

An interesting screw here is a variable length break-off knob screw. If you do not know exactly what lengthscrew will work, order these and break them off where you need them. A unique design allows this to be donewithout damaging the threads.

This chart lists the dimensions of wood screws and the closest fractional equivalents.

Shank Diameter Root Diameter

GaugeNumber

Max. HeadDiameter

Basic DecimalSize

NearestFractionalEquivalent

AverageDecimalSize

NearestFractionalEquivalent

ThreadsPer Inch

0 .119 .060 1/16 .040 3/64 32.00

1 .146 .073 5/64 .046 3/64 28.00

2 .172 .086 3/32 .054 1/16 26.00

3 .199 .099 7/64 .065 1/16 24.00

4 .225 .112 7/64 .075 5/64 22.00

5 .252 .125 1/8 .085 5/64 20.00

6 .279 .138 9/64 .094 3/32 18.00

7 .305 .151 5/32 .102 7/64 16.00

8 .332 .164 5/32 .112 7/64 15.00

9 .358 .177 11/64 .122 1/8 14.00

10 .385 .190 3/16 .130 1/8 13.00

11 .411 .203 13/64 .139 9/ 64 12.00

12 .438 .216 7/32 .148 9/64 11.00

14 .491 .242 1/4 .165 5/32 10.00

16 .544 .268 17/64 .184 3/16 9.00

18 .597 .294 19/64 .204 13/64 8.00

20 .650 .320 5/16 .233 7/32 8.00

24 .756 .372 3/8 .260 1/4 7.00

* Shank diameter is measured on the smoothportion of the screw above the threads.

* Root diameter is measured between the threadsand does not include the thread height.

11/10/11 Woodscrew Specifications - Autonopedia

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Basic types of wood screws

Wood screws are classified by the type of drive, the shape of head, its length and whether it is designed forwood or metal; this page refers to wood screws only.

Types of drive. The two basic drive designs are single slot and crosshead,crossheads are normally either 'Philips' or 'Pozidrive', these require specific types of screwdriver although aPhilips driver can be used on Pozidrive screws. It is always important to use the correct size of screw driver toensure that the workpiece and screw are not damaged.

Head shapes.

Countersunk heads can be concealed below the woods surface; raised heads are countersunk with a slightdomed head; round heads rest on the surface.

Threading on the shank is designed specifically for wood; wood threads have a tapped screw while sheet-metalscrews have mainly a parallel thread. Wood type screws are also normally used for securing into wall plugs.Screws for chipboard usually have 2 threads the full length of the shank.

Screw sizes.

Screws are sized by gauge number and length. The gauge number was thought up by someone with a weirdmind, if the gauge is not known, simply measure the diameter of the head in sixteenths of an inch, take awayone and double - that is the gauge number.

Example:

if the head is a quarter of an inch, that equates to 4 sixteenths;take away 1 equals 3;double that equals 6, so it is a 6 gauge screw.The length of screw is taken from the surface of the material to the point of the screw.

.And here is that famous break-off knob screw. Break-off screw 8-32 x 1 /34" zinc plated. Break-offpoints 1", 1 1/4", and 1 1/2".Perfect solution when your not quite sure which screw length you require.Simply grip the section below the break point you choose with a pair of pliers, and break off.Do not grip threaded section you want to use with pliers as this would damage the threads.

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