When choosing the correct screws for a job it’s important to know how to read the screw size. Having the right fasteners for your project will help ensure the proper hold and longevity. There are several factors to consider when determining the proper screw sizes, such as the diameter and length.
Screws are available in a variety of lengths and sizes, with each type of screw being categorized by the materials into which it will be screwed. For instance, wood screws have different threads than drywall screws, and each screw has its own specific purposes. For example, a wood screw with coarse threads is better for holding materials together while a fine threaded screw is more suitable for joining drywall to metal shafts.
Besides the diameter and threads, the length of a screw is also important to determine. The length will affect how deep the screw will be inserted into your material, and a long screw may require more force to drive in than a short screw.
Screws can be categorized by gauge, threads per inch (TPI), and shaft length in inches. For example, a screw that is labeled 6-32 x 1 1/2″ has a gauge of 6, threads per inch of 32, and is an inch and a half long.
Using a caliper, measure the distance between the peaks of the threads in the center of the screw. Then divide the number by the gauge, to get the thread pitch. A finer thread will have a lower thread pitch, and a coarser thread will have a higher one. 3/16 to decimal