Screw threads are one of those important elements of mechanical design that are often taken for granted but find usage in critically important applications. There is a very complex science behind applications of threads—even thinking about it can send shivers down the spine of the most astute mechanical engineer. The large spread of applications requiring threaded parts come with such a variety of performance requirements that one can get lost in some of the principle design functions such as how a threaded part is assembled to a matching part, how a threaded part performs under different operating conditions, and the strength of the threaded components.
As an example, screw threads are composed of many design elements that distinguish them from parts with a plain cylindrical shaft or hole but, in reality, the basic shape of a threaded mechanical element is the cylindrical shaft or hole. While there are many elements involved in checking screw threads, as there are different machines used to verify thread dimensions, most of the verification process comes down to a few critical dimensions, such as pitch diameter and major diameter, that can be measured and certified using master threaded rings and plugs. Just like master gage blocks provide the basis for dimensional measurement, master threaded plug and ring gages are the fundamental tool used to verify that an internal or external thread of a work piece is correct.