When choosing screw sizes, you must consider the thickness of the material you are attaching to and how much weight the screw will have to support. Thicker screws will be able to hold more weight, but they also take longer to drive in and are harder to remove. For general construction and woodworking, 8-gauge screws are a common choice.
Screws are also measured by their major diameter (also known as the shaft size) and thread count, which determines how close together the screw’s threads are. For example, a screw with a diameter of 1/4″ has a thread count of 20 threads per inch. The major diameter and the thread count combine to determine a screw’s gauge, which ranges from 0 to 12.
Some types of screws are also measured by their length. Non-countersinking screws are generally measured from just under the head to the tip. This includes hex-head, pan-head, button-head, round-head, and truss-head screws. Countersinking screws, on the other hand, are measured from the base of the countersink to the head.
Screws may be labeled with measurements in the imperial system or metric system, depending on where and when they were manufactured. Screws that use the imperial system will typically list their gauge first and then their length, with the threads per inch listed between them. For instance, a package of hex-head screws will list the gauge number followed by the diameter and length, such as 10 x 2″. Screws that use the metric system will usually list the diameter first and then their length, such as 5.0 x 60. 15mm in inches