Thread Plug Gauge Buyer's Guide

1. Internal Thread Plug Gauges

1.1 Use of internal Thread Plug Gauges GO

A thread plug gauge of internal GO threads checks theoretical size of the internal thread (measurement of the theoretical - pitch diameter ). This is achieved by inspecting the minimum pitch diameter, taking into account pitch errors, side angle errors and form deviations, which cause an apparent reduction in the workpiece pitch diameter (theoretical pitch diameter). In addition, it helps to check the minimum limit of the major diameter and also whether the length of the straight side is sufficient. i.e. that the rounding at the root of the profile does not interfere too much with the side of the thread. This measuring instrument does not help to inspect the small diameter of the workpiece thread. The GO thread plug gauge, when screwed in by hand without using excessive force, enters the entire length of the thread of the workpiece to be tested. If penetration is not possible, the thread of the part does not meet the specifications.

1.2 Use of NOGO thread plug gauge for internal threads (marked in red)

A internal thread gage tester NOGO checks if the actual pitch diameter exceeds the specified maximum size.

THE internal thread tester NOGO, when screwed by hand without using excessive force, can enter both ends of the threaded part, but not more than two threads. If it can be screwed with more than two threads, the thread does not meet the specification.

2. External Thread Checkers

2.1 Using an external thread tester with GO rings

A GO external thread ring gauge checks the virtual size of the external thread (measurement of the theoretical pitch diameter). i.e. it inspects for the maximum material limit of the pitch diameter, taking into account the deviations of the form and pitch errors and the side angle errors, which produce an apparent enlargement of the pitch diameter of the workpiece.
It also helps to check that the maximum small diameter has not been exceeded.
The major diameter of the external thread is not being checked from this meter.
The GO thread ring gauge, when screwed in by hand without using excessive force, should pass the full length of the workpiece thread. If assembly is not possible, the threading of the part does not meet the specifications.

2.2 Using the NOGO external thread ring gage (with red mark)

A NOGO external thread ring gauge is intended to check whether the actual pitch diameter of a workpiece exceeds the specified minimum size. A NOGO external thread ring gage, when screwed in by hand without using excessive force on the thread of the workpiece, can enter both sides but not more than two threads. If the gauge can be screwed onto the workpiece with more than two threads, the thread is out of specification.