In woodworking, it is important to have the correct screw size for a project. However, determining the proper screw size can be complicated when there are many factors involved such as the type of wood, head-bore vs shank-hole size, and lateral vs sheer forces. The use of a screw chart can help make the process easier. It also helps to understand the intricacies of the screw sizing system, such as gauge and threads per inch (TPI).

A screw’s size is determined by its diameter, or the width of its threaded portion. Its diameter can be measured with a ruler or measuring tape. For example, a #8 screw has a diameter of 0.17″ and a TPI of 8 threads per inch.

When a screw is inserted into wood, it creates pressure against the board’s fibers, which grip the screw’s threads and hold it in place. The force exerted by this grip is what gives a screw its power. If the screw is inserted too deep, it can cause damage to the wood fibers and reduce its strength. A screw that is too short may not be able to reach the wood’s underlying material, while a screw that is too long will protrude through the surface and could be dangerous to use.

The first number on a screw’s gauge, or thickness, indicates its diameter, while the second number refers to its head-bore size or the diameter of the smooth portion of the screw above its threads. A screw’s head-bore size is usually less than the diameter of the shank, but can be as large as the entire diameter of the screw. A screw with a larger head-bore than the shank diameter is known as a countersunk screw.

There is no direct correlation between a screw’s gauge and its head-size, except for the fact that from gauge 6 and above, the diameter of the head is approximately equal to half of the screw’s gauge. However, this is a rule of thumb and may not always be accurate. In most cases, the head-size is not listed on a screw’s packaging.

Lastly, it is essential to know what type of drywall you are using. The most common drywall used in residential construction is 1/2-inch thick, while a thinner 1/4-inch drywall is sometimes used to cover curved surfaces or for soundproofing purposes. Thicker drywall, such as 5/8-inch thick Type-X drywall, is typically used in commercial construction and is required for certain fire codes in some buildings. This type of drywall requires different sheetrock screws than regular drywall.

When purchasing screws, check the box label for both imperial and metric measurements, which are often listed together on the same chart. In addition to the screw’s gauge and TPI, the box label should specify whether it is a drywall screw or not.

The UTS screw chart is a comprehensive reference that includes both imperial and metric screw sizes along with their respective mm sizes. It provides a quick and easy way to convert imperial screw sizes to metric screw sizes and vice versa. In addition, the chart explains the relationship between a screw’s gauge and its threads per inch (TPI) and how to read it. 1/4 screw diameter