A Standard Thread Plug Gage refers to an inspection tool used to check a workpiece against its allowed tolerances via a go/no-go test.
For example, ISO 1502 sets a standard for screw threads and gaging to test them. It establishes the attribute T as go for the major diameter and the attribute Z as no-go for the pitch diameter. The inspection tool has two threaded components. For example, there would be two female sections on a gauge to test a threaded male workpiece such as a screw. If the major diameter of a screw is too large, it will not fit in the T test thread at all (fail). If the major diameter is too small, the fit is sloppy (fail). If the thread has been cut too deep, it screws into the Z test thread (fail). If it is the right size and only does about three turns, the fit is right (pass).
These Thread Plug Gages are an integral part of the quality process that is used in the manufacturing industry to ensure interchangeability of parts between processes or even between different manufacturers. It does not return a size or actual measurement in the conventional sense, but instead returns a state, which is either acceptable (the part is within tolerance and may be used) or unacceptable (the part must be rejected).
Each of the set listed below include a GO / NO GO gage.