Screws are an essential part of construction jobs and can be used to hold materials together in a wide range of applications. Choosing the correct size and type of screw for your task is important, as the wrong screw can break materials or damage electrical wiring or pipes in walls and floors. A screw that is too short won’t hold materials together, while one that is too long could go right through the material and break it or cause structural issues.
Screw measurements are usually shown on the packaging using three numbers. The first number is the screw’s gauge, which is a measure of the diameter of the screw thread. A gauge of 0 is the thinnest and a gauge of 12 is the thickest. A screw’s length is also important, as a longer screw may need to penetrate deeper into the material than a shorter screw.
The last number, which is the threads per inch (TPI), is a measure of how many threads are on one inch of screw. So, a screw that is labeled 6-32 x 1 1/2" means it has a #6 gauge and 32 threads per inch.
Screws can be measured using the metric or imperial system, and there are conversion tables available to help you match up measurements. The table below provides a conversion from metric to US fraction and from imperial to metric mm for screws sizes up to 4". The chart is broken down into coarse (UNC) and fine thread (UNF) categories. pilot hole for 3/8 lag screw