ISO 1502 sets a standard for threads and gauging 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.[1] 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 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 the thread has been cut too deep, it screws into the Z test thread (fail). If the fit is right and only does about three turns (pass).[2]
A go/no go gauge is 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).
They are well suited for use in the production area of the factory as they require little skill or interpretation to use effectively and have few, if any, moving parts to be damaged in the often hostile production environment