How do I test a female thread? – Thread limit plug gauge

Testing internal threads: the thread limit plug gauge

How do I check the quality of an internal thread quickly, safely and economically? Of course you can measure all five important thread sizes individually. Each size is recorded numerically. This is time-consuming and error-prone. It is better to use thread gauges. That is why we would like to introduce the appropriate tool for this purpose today: the thread limit plug gauge.

It is a combination of a “good” plug gauge according to DIN 2281/2282 and a “reject” plug gauge according to DIN 2283/2284 The bodies are attached to the left and right of a gauge handle. The reject side is marked with a red ring for better differentiation.

Reject plug gauge according to DIN 2283/2284 = red | good plug gauge according to DIN 2281/2282 = without marking

The procedure for using the thread plug gauge

When you have finished cutting a thread, you must first clean the thread and remove lubricant residues. Only a clean thread will give reliable results. Please also pay attention to the temperature. It should be around 20 degrees. Higher temperatures can falsify the test results.

Then take the thread limit plug gauge in your hand and carefully screw the “good side” into the thread. This should be possible without any particular effort and the screwing process should cover the entire length of the thread.

If this works as described, then we know the following: the minimum outer diameter and flank diameter are within the prescribed tolerance. The mating dimension of the thread is correct.

Now the other side is used. It is marked with a red ring. Now screw the reject side into the thread. Please do not apply any force. Ideally, it should only be possible to move the reject side into the thread by 2 turns. The evaluation of the number of revolutions takes place during unscrewing.

The reject plug gauge checks the flank inside diameter for exceeding the maximum dimension.

It doesn’t work that way:

If you are able to screw in the reject body more than three gears, then it is rejects. This can have various causes.

More about the errors in threading, you will find in this article:

https://threadingtoolsguide.com/en/blog/problems-with-thread-cutting/

Video instructions for the limit plug gauge

First cut on thread limit plug gauge

Unlike taps or dies, a thread limit plug gauge has no chamfer.

Thread limit plug gauges are manufactured in such a way that the start of the thread begins at the core diameter so that the thread can be measured from the first turn. This means that the thread limit plug gauge can be used to determine the useful length of the cut thread without further ado.

If you have any questions about the thread limit plug gauge, we look forward to hearing from you. Please write to us under info [@] gsr-germany.de. We will be happy to advise you!