The previous two columns dealt with a study of thread plug gage calibration, the results of which will be discussed and/or argued over for some time. Not to be left out, the adjustable thread ring gage provides plenty of fodder for arguments about how ‘good’ their calibration is in practical terms.
The ASME standards to which these gages are made require them to be verified by their fit on an appropriate setting plug. There is no other option on the smaller sizes but different hardware for directly measuring pitch diameter is often used to get around the costs of a setting plug for non-stocked gages. Each method takes a different approach to the situation and because they are not the same from a metrology point of view, the ‘answers’ they produce are rarely the same either.