Tapered Pipe Threads

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On your docket today in your inspection department one product you must inspect and verify is a part with a Tapered Pipe Thread. Does not sound too tough, but did you know that there are actually three different common Tapered Pipe Threads used in industry today?

Though they are similar in design, they are very different in not only how they are used, but also how they are gaged.

NPT (National Pipe Taper) is the simplest form of Tapered Pipe thread. These have a 60 thread form and a taper of .750” per foot. Typically used with a sealing compound or tape, the fittings are basically tightened until they don’t leak as the threads themselves form the seal as opposed to straight threads which just hold the components together. One Thread Gage is used to verify the thread, whether internal or external. NPT fittings are normally used for low-pressure applications and in the home plumbing.

ANPT (Aeronautical National Pipe Taper) is identical in thread form and taper as the NPT but because of critical applications used by the Army and Navy a strict gaging procedure is used which includes two (2) Thread gages and one (1) plain diameter gage to make sure all of the aspects of the thread are closely scrutinized.


NPTF (National Pipe Taper Dryseal/ Fuel) is also the same form and taper as the two aforementioned but with the NPTF thread these parts have a controlled “Flat” on both the root and crest of the threads and this is where they make their seal. These are used for higher pressures and where the parts need to be taken apart from time to time without worry of leakage. No sealant is necessary with NPTF thread. These also use a 3-gage system for verification and are gaged similar to the ANPT thread but the gages are completely different in design.

This is a lot of information to digest at one sitting but that is what the staff at Gaging.com LLC prides themselves in. With decades of combined knowledge in the Measuring Tool Industry including any type of Functional or Thread Gauge we can assure you that your questions will be addressed and answered with the ease of a phone call or message.

There will be more to come on Thread Gauging applications and solutions in the near future.

Last update: Jun 10, 2013


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