Why do we use Teflon Tape with NPT?

There are a variety of pipe thread types that can be used in the world of fittings, valves, and threaded pipes but the two most popular are NPT and NPTF.

NPT Valve

NPT stands for national pipe thread and is by far the more common of the two thread types used in valves. NPTF stands for national pipe taper fuel. NPTF is also sometimes referred to as Dryseal American National Standard Taper Pipe Thread.

NPT measurements are sometimes referred to as FIP (for Female Iron Pipe), MIP (Male Iron Pipe), MPT (Male Pipe Thread), FPT (Female Pipe Thread) and IPT (Iron Pipe Thread).DuraChoice 3 way ball valve with NPT thread.

At first glance both threads appear to be similar. They both have a ¾” taper over 1 foot of length. They both have the same pitch diameter at the top of the hole of threads internally or the end of the pipe on external threads.

That being said, there are significant differences that must be taken into consideration.

The primary difference is in the minor and major diameters, the crest and root of the threads.

NPT threads are designed to be used with a sealing compound such as Teflon tape to create a leak-free seal, whereas NPTF threads form a mechanical seal by crushing the entire thread form.

If NPT is used without a sealing compound then there can be leakages or other unpleasant issues.


NPT will work great for most of the normal applications and the vast majority of valves are in NPT.

Only in mission critical situations (e.g., fire systems or aviation) would NPTF be a better choice. It should be noted however that NPTF is much less common and much more expensive.

NPT and NPTF threads can be used together, as long as an appropriate sealant is used.

It is important to discuss the difference because if you are adding this valve to an existing system, you have to be sure you are getting the right thread type.

If you don’t review these details then you may purchase the wrong valve or fitting for the wrong application and you may experience leakages which will cost you more money.