Screws come in a variety of shapes and sizes with different thread patterns designed for different types of materials. Using the right type of screw for the job helps maximize its durability and improves the ease with which it can be installed. It also helps reduce the likelihood that the screw will come loose, which can lead to a project’s failure and require a costly replacement.
Screw sizing is generally expressed as the gauge (a measure of the screw’s external diameter) followed by the number of threads per inch and the shaft length in inches. For example, the dimensions for a wood screw would be 6-32 x 1 1/2″. The middle number refers to the “normal” number of threads per inch for that screw diameter, and the last number is the length in inches.
The thread pattern on a screw is generated by subtractive methods like cutting [single-pointing, taps and dies, milling]; molding and casting [sand casting, single-point molds]; and forming. Additive methods include thread rolling and extruding, as well as combinations of these techniques.
A screw’s diameter and thread pitch can be determined by examining it with a thread gauge, which is a strip of metal that has a range of thread sizes cut into it. By moving the screw in a hole in the material that it will be screwed into, you can systematically work your way through the gauge to find the thread that matches up. A digital caliper can also be used to match up the screw head size with a thread scale on a nut or bolt. 3/16 to decimal