How to Use a Thread Plug Gauge Correctly

To use a thread plug gauge, screw the GO member into the thread by hand, then try the NOT-GO member. The part passes only if the GO member goes in fully and the NOT-GO member does not.

Steps

1. Clean the thread and the gauge, and remove burrs and chips. 2. Hold the GO member square to the hole and start it by hand. 3. It should screw in for the full length of the thread without excessive force. 4. Try the NOT-GO member. It must not enter more than two turns from either end. 5. If both conditions are met, the thread is within tolerance.

Common mistakes

Forcing the gauge in, using it as a tap, checking a dirty or oily thread, or using a worn gauge can all give a false result. Do not use a gauge that has been dropped or damaged.

Calibration

A gauge wears with use, so it should be checked against its certificate. See what traceable calibration means.