NPT thread - chart, dimensions, how to measure

What is an NPT thread?

An NPT thread is an inch tapered thread with a 60-degree profile angle, a 'V' shape and a flattened crest. The abbreviation itself refers to 'National Pipe Tapered Thread'.

It appeared in 1864 in America, where it was established as a national standard by William Sellers.

It is worth mentioning here that there is another name for NPT - the Briggs tapered pipe thread. Therefore, if you were to come across one, know that it is the same thread.

On the market you can also find the NPS thread, which is also an American thread, but cylindrical (not tapered). However, it is much less commonly used.

What is the application of the NPT thread?

The main application of the NPT thread is a joint of a sealing nature in various hydraulic, pneumatic, etc. installations. Due to the origin of this thread type, you will most often encounter it in Canada and the United States, but it is popular all over the world.

The joint works on the principle that the external thread pulls the internal valve, so that the system maintains the correct pressure.

What are the dimensions of NPT threads? NPT thread chart

Below, we have collected the dimensions of NPT threads:

How to measure a NPT thread?

You can measure NPT threads with a calliper.

When it comes to the outer diameter, simply grip the thread at its widest point with the jaws of the tool and read the result. You will measure the inner diameter similarly, but in this case use the smaller jaws of the calliper.

The measurement of the thread pitch is done a bit differently. In this case, put the jaws of the calliper parallel to the thread so that each jaw is adjacent to a separate of the thread crest.

The best way is to do this over a space of 5 crests, and divide the result by 4 (why 4? Because you are dividing by the number of roots between the crests). The resulting number is the pitch of the given thread.

Compare it with the chart and see which NPT thread you need!