NPT & NPS Threads

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National Pipe Taper (NPT) & National Pipe Straight (NPS) Threads

NPT & NPS THREADS

NPT NATIONAL PIPE TAPER (AMERICAN) Thread form per ANSI/ASME B1.20.1
NPS NATIONAL PIPE STRAIGHT (PARALLEL) Thread form per ANSI/ASME B1.20.1
NPTF NATIONAL PIPE TAPER FOR FUEL Thread form per SAE J476
NPSM NATIONAL PIPE STRAIGHT MECHANICAL Thread form per ANSI/ASME B1.20.1
NPT NPS Threads
Click image to enlarge.
National Pipe Thread (NPT) is a family of technical standards for threads that has been adopted internationally for interconnecting hoses and fittings by mating an external (male) thread with an internal (female) thread. National Pipe Threads are similar in function to BSP threads, but are not generally interchangeable. They include both tapered and straight thread series for various purposes including rigidity, pressure-tight sealing, or both. The various types include NPT, NPS, NPTF and NPSM.

There are four types of NPT threads:

  • National Pipe Taper (NPT)
  • National Pipe Straight (NPS)
  • National Pipe Taper For Fuel (NPTF)
  • National Pipe Straight Mechanical (NPSM)
NPTF threads (also known as Dry Seal) are an improvement to NPT.

Controlled truncation of threads mean the metal-to-metal thread seal is at root and crest of threads, in addition to flanks of threads.

Measure NPT male thread OD and NPT female thread ID at first full thread near end of fitting.

For More Information:
Read our guide: Thread & Connector Working Pressures.
Additionally, don’t hesitate to contact your local RYCO Hydraulics Customer Service representative or fill out our contact form to learn more about BSP threads.

NPT Threads Dimensions

NPT THREAD
SIZE & PITCH
DASH
SIZE
MALE THREAD
MINOR OD
FEMALE
THREAD ID
 inch – TPI mm inch  mm inch
1/8 – 27 -02  9,9  0.39 8,4  0.33
 1/4 – 18 -04 13,2  0.52  11,2 0.44
3/8 – 18  -06  16,6  0.65 14,7 0.58
1/2 – 14 -08 20,6 0.81 17,8 0.70
3/4 – 14 -12 26,0 1.02 23,4 0.92
1 – 11.1/2 -16 32,5 1.28 29,5 1.16
1.1/4 – 11.1/2 -20 41,2 1.62 38,1 1.50
1.1/2 – 11.1/2 -24 47,3 1.86 43,9 1.73
2 – 11.1/2 -32 59,3 2.33 56,4 2.22
2.1/2 – 8 -40 71,5 2.82 69,1 2.72
3 – 8 -48 87,3 3.44 84,8 3.34

NPSM Threads Dimensions

NPSM THREAD
SIZE
DASH
SIZE
FEMALE
THREAD ID
inch – TPI mm inch
1/8 – 27 -02 8,6 0.34
1/4 – 18 -04 11,9 0.47
3/8 – 18 -06 15,0 0.59
1/2 – 14 -08 19,1 0.75
3/4 – 14 -12 24,6 0.97
1 – 11.1/2 -16 30,5 1.20
1.1/4 – 11.1/2 -20 39,4 1.55
1.1/2 – 11.1/2 -24 45,5 1.79
2 – 11.1/2 -32 57,4 2.26
2.1/2 – 8 -40 68,8 2.71
3 – 8 -48 84,6 3.33
Thread size refers to the nominal bore of the pipe.
Subtract approximately 1/4”(6 mm) from thread measurement for nominal pipe size.
Pitch is Threads Per Inch (TPI).