Screw sizes are more than just a technical detail — they’re critical for creating strong, secure connections that can hold the load required for your project or repair work. Choosing the wrong screw size can lead to poor results, including weak or unreliable joints. But correctly measuring screw sizes is easy with the right tools. The most important measurement is the diameter of the screw’s shaft, which tells you if it will fit the hole into which it will be installed. Other measurements are the length and the thread pitch, both of which can affect the strength and compatibility of your screws with the material they’re being used for.
Most screws are sized according to their major diameter, which can be determined by looking at the screw’s packaging. This number represents the screw’s outer diameter and is typically listed in millimeters, while imperial screws use a letter-and-number system (from #12 to #0000, which is super tiny). The second number in the designation is the thread pitch, or how many threads per inch the screw has. Screws with larger pitches have coarser threads, while those with smaller pitches have finer ones.
Finally, the length of the screw will be listed as the distance between the tip of the head and the underside of the screw’s shank. The length is often important, as it can indicate if the screw will stick out too far and damage the material, or if it will penetrate fully through the materials. This can be determined by using a ruler or tape measure, or a more precise tool like a caliper. pilot hole for 5/16 lag screw