A pair of precision thread plugs, usually on one handle, used to accept or reject tapped holes and nuts. The GO member must turn in by hand for the full length of engagement, proving the thread is large enough and correctly formed, while the NO GO member may start but should not enter more than about three turns, proving pitch diameter is not oversize. External threads are checked the same way with GO and NO GO ring gauges.
GO end of the thread plug gauge went in all the way, NO GO stopped at a turn and a half, so the holes are good, stamp the traveler.
Never force a thread gauge; if the GO member needs a wrench, the part fails and the gauge just lost some of its life.
Also heard as
- GO/NO GO gauge
- thread plug
Related terms
Pitch diameter
The diameter at which thread thickness equals the gap between threads, the dimension that controls fit.
Thread class
A number-and-letter grade, such as 2A or 3B, that sets how much tolerance and allowance an inch thread has.
Class 3A/3B
The tightest standard inch thread fit, with no allowance on the external thread, used for precision hardware.