National Pipe Thread Taper (NPT) is a US Standard for tapered threads used on threaded pipes and fittings. In contrast to straight threads that are found on a bolt, a taper thread will pull tight and therefore make a fluid-tight seal.

National Pipe Taper Fuel (NPTF), also called Dryseal American National Standard Taper Pipe Thread, defined by ASME B1.20.3, is designed to provide a more leak-free seal without the use of teflon tape or other sealant compound. NPTF threads are the same basic shape but with crest and root heights adjusted for an interference fit, eliminating the spiral leakage path.

  • The Angle Between The Taper And The Center Axis Of The Pipe Is 1o 47′ 24” (1.7899o)
  • Truncation Of Roots And Crests Are Flat.
  • 60o thread angle
  • Pitch Is Measured In Threads Per Inch

Note! Pipe sizes do not refer to any physical dimensions. The outside diameter of a pipe or fitting must be measured and compared to a table for size identification. A 3/4″ NPT pipe thread has an outside diameter – OD – of 1.050 inches.

Each thread size has a defied number of threads per inch – TPI, or pitch. The 3/4″ NPT pipe thread has 14 threads per inch. Both the TPI and OD of the thread are required for positive identification of thread size because more than one size have the same TPI.

NPT threads are not interchangeable with NPS – National Pipe Straight – threads.

NPT threads may look similar to ISO 7/1 threads. However, ISO and NPT threads should not be mixed. ISO threads have 55o  taper angle versus 60o  for NPT. The NPT root and crest configurations are also different from ISO. For ISO threads pitch is usually measured in mm (may be expressed in Inch) The pitch are different.

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