NPT Thread Fitting

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NPT Thread Fitting

Fluid Tech Group is the first enterprise in northern China specializing in exporting fire protection system pipe fittings. We have five production bases in Tangshan, Hebei; Weifang, Shandong; Cangzhou, Shanxi; and Zhejiang. We offer one-stop procurement, coordinating production, inspection, loading, and delivery.

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What Does NPT Mean in Threads?

NPT stands for National Pipe Tapered, a standardized thread type used in plumbing and piping systems. The tapered shape of NPT thread fitting locks the threads as they tighten. This creates a tight, leak-proof seal.

Special Qualities of NPT Thread Fitting

1. NPT Thread Design

  • NPT threads are tapered, which means that as the pipe lengthens, the threads’ diameter gets smaller.
  • When two linked sections of pipe or fittings are tightened, the tapered design of the threads compresses the thread edges against one another, improving the seal between them.
  • Leak prevention is aided by the threads’ rising angle when the connection is made.

2. Thread Angle and Geometry

  • NPT threads typically have a 60-degree thread angle, which is the angle between the thread sides.
  • The sharp, angular profile enhances the sealing action. Tightening the threads deforms them slightly, creating a seal.
  • The angle ensures a strong mechanical connection between mating parts.

3. Mechanism of Sealing

  • NPT threads rely on metal-to-metal contact to form a seal, unlike straight threads.
  • Thread sealing compounds or Teflon tape improve the seal and prevent leaks.
  • The taper of the threads creates a wedging action, tightening the connection as the joint is screwed in.

Standard Npt Thread Sizes

Nominal Pipe Size Thread Size (NPT) Outer Diameter (OD) (inches) Threads Per Inch (TPI) Pitch (mm)
1/8″ 1/8″ NPT 0.405 27 0.94
1/4″ 1/4″ NPT 0.540 18 1.41
3/8″ 3/8″ NPT 0.675 18 1.41
1/2″ 1/2″ NPT 0.840 14 1.81
3/4″ 3/4″ NPT 1.050 14 1.81
1″ 1″ NPT 1.315 11 2.30
1-1/4″ 1-1/4″ NPT 1.660 11 2.30
1-1/2″ 1-1/2″ NPT 1.900 11 2.30
2″ 2″ NPT 2.375 11 2.30
2-1/2″ 2-1/2″ NPT 2.875 8 3.18
3″ 3″ NPT 3.500 8 3.18
4″ 4″ NPT 4.500 8 3.18
6″ 6″ NPT 6.625 6 4.23

ANSI NPT Thread Standard​

The American National Standards Institute (ANSI) and the American Society of Mechanical Engineers (ASME) define the NPT thread standard. NPT threads are also known as NPTF (National Pipe Tapered Fuel) or NPT Class. The specific type and application determine the designation.

Differences between NPT and BSPT Threads

  • NPT threads differ from BSPT threads, commonly used in the UK and other regions.
  • Both have a tapered shape but differ in thread angle, pitch, and diameter.
  • NPT threads use a 60° angle, while BSPT threads typically have a 55° angle.

NPT threads are widely used in fire fighting pipe fittings and systems handling pressurized fluids or gases. NPT thread fittings serve in industrial piping, natural gas, water systems, hydraulic systems, and compressed air lines.