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Wood Screw Specifications

Here you may select the appropriate screw for your project. Some of those pesky technical descriptions are necessary: The terms "phillips", "square drive", "slotted", and "truss head", refer to the kind of driver used to turn 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, but may be the same length. This is important. Most wood screws have a common "pitch" to the threads, but some have 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" refers to the size (diameter) of the screw, and the "32" means it has 32 threads to the inch. And then, the are those termed "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 length screw will work, order these and break them off where you need them. A unique design allows this to be done without damaging the threads.

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

screw information

Shank Diameter Root Diameter
Gauge Number Max. Head Diameter Basic Decimal Size Nearest Fractional Equivalent Average Decimal Size Nearest Fractional Equivalent Threads Per 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 smooth portion of the screw above the threads. * Root diameter is measured between the threads and does not include the thread height.

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 for wood or metal; this page refers to wood screws only.

Wood screw drives 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 a Philips driver can be used on Pozidrive screws. It is always important to use the correct size of screw driver to ensure that the workpiece and screw are not damaged.

Types of wood screws Head shapes.

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

Threading on the shank is designed specifically for wood; wood threads have a tapped screw while sheet-metal screws 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 weird mind, if the gauge is not known, simply measure the diameter of the head in sixteenths of an inch, take away one and double - that is the gauge number.

Example:

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