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NPT and NPTF tapered pipe fittings

American tapered pipe thread with a 60° form. Seals on the thread itself; NPT needs sealant, NPTF is the dry-seal version.

  1. JIC 37°
  2. ORFS
  3. BSP
  4. NPT
  5. Metric DIN
  6. JIS / Komatsu
  7. O-ring boss
  8. SAE flange

What it is

NPT is a tapered thread: both male and female narrow at 1 in 16 on diameter, so they wedge tighter as they are screwed together. The seal is made by the threads themselves.

Standard NPT leaves a spiral leak path at the crests and needs tape or sealant. NPTF, the dry-seal form used in hydraulics, has controlled crests and roots that crush together to seal without sealant, though sealant is still often used.

Thread
Tapered, 60° form, counted in threads per inch
Seal
Thread flanks wedge together; NPT requires sealant
Standard
ASME B1.20.1 (NPT), SAE J476 / ASME B1.20.3 (NPTF)
Also called
National pipe taper, pipe thread, dry-seal (NPTF)

What it looks like

Tapered thread — seals on the thread itselfHex
Tapered thread seals on its flanks. Male end shown; the sealing surface is orange. Illustration, not to scale.

How to recognise it

  1. The male thread visibly narrows toward its end.
  2. There is no cone, flat face or O-ring.
  3. Thread angle is 60° with flattened crests.
  4. The size name is nominal pipe size: 1/2 in NPT measures about 21.3 mm across.

Where it is used

Common on North American equipment for ports, gauges, pipework and older machines. It is being replaced on new hydraulic designs by O-ring connections, because tapered threads are prone to leaks and can crack a port if overtightened.

Size chart

NPT / NPTF tapered pipe — ASME B1.20.1 (NPT), SAE J476 (NPTF)
SizeThreadMale thread OD (nominal)Pitch
1/8 in1/8-27 NPT10.29 mm / 0.405 in27 TPI
1/4 in1/4-18 NPT13.72 mm / 0.540 in18 TPI
3/8 in3/8-18 NPT17.15 mm / 0.675 in18 TPI
1/2 in1/2-14 NPT21.34 mm / 0.840 in14 TPI
3/4 in3/4-14 NPT26.67 mm / 1.050 in14 TPI
1 in1-11.5 NPT33.40 mm / 1.315 in11.5 TPI
1-1/4 in1-1/4-11.5 NPT42.16 mm / 1.660 in11.5 TPI
1-1/2 in1-1/2-11.5 NPT48.26 mm / 1.900 in11.5 TPI
2 in2-11.5 NPT60.33 mm / 2.375 in11.5 TPI

Measure a tapered thread at the fourth or fifth full thread from the end.

Match a measured thread with the thread identifier →

Commonly confused with

BSPT
Also tapered. BSPT has a 55° thread angle and different threads per inch in most sizes: 1/4 in is 18 TPI in NPT and 19 in BSPT.
NPSM
A parallel American pipe thread with the same pitch, used on swivel nuts with a 30° seat.
SAE O-ring boss
Port thread on the same machines, but parallel with an O-ring.

Interchangeability

NPT and NPTF share dimensions and can be assembled together, sealing as NPT with sealant. NPT does not interchange with BSPT.

Frequently asked questions

What is the difference between NPT and NPTF?

Both have the same taper, pitch and diameters. NPTF has tighter control of the thread crests and roots so they seal metal to metal without sealant. NPT always needs sealant.

How do I measure an NPT thread?

Measure the outside diameter at about the fourth full thread and count threads per inch. 1/2 in NPT is about 21.3 mm with 14 TPI; 1/4 in is about 13.7 mm with 18 TPI.

Why are NPT fittings being replaced in hydraulics?

Tapered threads rely on deformation to seal, loosen with vibration and temperature cycling, cannot be positioned at a set angle without over- or under-tightening, and can split a port. O-ring connections avoid these problems.

Related

Dimensions are nominal reference values. Confirm against the standard or the fitting manufacturer before ordering.

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