Thread Plug Gauge vs Thread Ring Gauge

A thread plug gauge checks an internal thread, such as a tapped hole or a nut. A thread ring gauge checks an external thread, such as a bolt, a stud or a threaded shaft. Both work as GO / NOT-GO limit gauges.

Thread plug gauge

The GO member of a plug gauge must screw into the hole by hand for the full length of the thread. The NOT-GO member must not enter more than two turns from either end.

Thread ring gauge

The GO ring must screw onto the thread by hand without excessive force. The NOT-GO ring must not screw on more than two turns from either end.

Which one do you need?

Look at the feature you are checking. A nut or tapped hole needs a plug gauge. A bolt or stud needs a ring gauge. If you make both mating parts, you need both, each to the same thread standard and tolerance class.

Still not sure?

Share the thread size and standard on our quote page and we will confirm the gauge.