When working on a project, there is nothing more frustrating than running out of the right kind or size of screw. Jaycon Systems engineers use screws for everything from connecting plastic parts together to mounting printed circuit boards to the frame of a machine, and it is important that we always have the right size on hand for each application.

One of the first things we do when ordering supplies is to review the specs for each type of screw. From there, we can select the best kind for the job at hand. Unfortunately, there is some confusion among woodworkers about what all the different kinds of screw sizes mean. For instance, plans and instructions refer to specific kinds of screws by their diameter and thread count (3/8-16) but what does this really mean? The answer depends on whether we are dealing with standard or metric screws.

The metric system uses millimeters (mm) to measure screw threads, and it is a little more complicated than the inch-based Unified Thread Standard system. In the metric system, you have to determine the threads per inch as well as the major diameter. To figure out threads per inch, you simply count the number of thread peaks along a one-inch length of the screw. To calculate the major diameter, you can use a ruler or caliper to measure the distance between two adjacent threads at their peaks. Then, add the two values together to get your screw size. For example, a screw with a major diameter of 6 mm and a thread pitch of 1 mm is a size M6.

While screw sizes may seem confusing, there is an easy way to understand them. The first number in the spec for a screw, as listed in a chart, is the shaft diameter of the screw, which is measured at its point closest to the head. The second number is the number of threads per inch on the screw's shaft, which relates to how tightly the screw will be wound by the wrench or driver. So, a screw with a shaft diameter of 1/4" and a thread count of 32 is a size 6-32.

The third number, usually located in the middle of the spec, refers to the screw's length. In the metric system, this value is specified by using the letter M, while in the UTS system it is usually just written as a decimal value. Screw length is important because it will determine how deep a screw can go into the material and whether it will interfere with its intended use. For example, a screw that is too long will protrude from the surface of a wooden bench while a screw that is too short won't penetrate the material at all. For this reason, we recommend using a screw length guide or calculator to ensure you are getting the correct screw for your project.screw size chart