Plug gauge

A go-no gauge (or go/no-go) refers to an inspection tool used to check a workpiece against its allowed tolerances. Its name is derived from two tests: the check involves the workpiece having to pass one test (go) and fail the other (no-go).

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. 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 the fit is right and only does about three turns, the fit is right (pass).

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.

These gauges are referred to as plug gauges; they are used in the manner of a . They are generally assembled from standard parts, where the gauge portion is interchangeable with other gauge pieces (obtained from a set of pin type and a body that uses the collet principle to hold the gauges firmly. To use this style of gauge, one end is inserted into the part first, and depending on the result of that test, the other end is tried.

In the right image, the top gauge is a thread gauge that is screwed into the part to be tested, the "GO" end should fully enter the part; the "NOT GO" end should not. The lower image is a plain plug gauge used to check the size of a hole; the green end is the go, and the red end is the no-go. The tolerance of the part that this gauge checks is 0.30 mm, where the lower size of the hole is 12.60 mm and the upper size is 12.90 mm, every size outside this range is out of tolerance. This may be initially expressed on the parts drawing in a number of styles; three possibilities may be

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