4.11 Thread Plug Gages
D.M. Donner
Thread plug gages are used to measure ID threads. Machine shops have a large inventory of thread gages due to the volume of threads available and the required class of fit.
Thread gages come in the go/no-go configuration with the no-go plug using a pitch diameter larger than the class of fit allows, and the go size set to the minimum thread pitch diameter for the class of fit. The thread gage above is for a ½ X 13 UNC 2B thread with a pitch diameter of .4500 for the go end, and a .4565″ pitch diameter for the no-go end.