External threads can be checked with the help of thread ring gauges.
With a GO thread ring gauge the flank diameter and the pitch deviation of a sample are measured.
Furthermore the core diameter can be tested. It is therefore a dimension gauge and a form gauge.
The testing sample needs to be screwed completely into the GO thread ring gauge without any particular extertion of force.
If this is not the case, the tolerances of the nominal dimension are not fulfilled.
A NOGO thread ring gauge is used to measure the falling below the specified minimum dimension of the flank diameter.
The NOGO thread ring gauge never fits on a perfect test sample. It is therefore only a dimensional gauge.
The reject (NOGO) side of the ring gauge is marked with red.