American National Standard Taper Pipe Thread (NPT)

AMERICAN NATIONAL STANDARD TAPER PIPE THREAD (NPT)

National Pipe Threading (NPT) ports are standardized ports for water and air lines. NPT fittings must be used with NPT ports, using different standards will damage the threads.

NPT Threads can be called sometimes as MPT, MNPT or NPT(M) for male external threads, and FPT, FNPT ot NPT(F) for female internal threads. Some of these names are not authorized designations per the ANSI standard.

For a leak tight connection a sealant compound or Polytetrafluoroethylene (PTFE) must be used.

IMPORTANT:

Nominal pipe size 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 1/4″ NPT pipe thread has an outside diameter (OD) of 0.540 inches.

Each thread size has a defined number of threads per inch (TPI). The 1/4″ NPT pipe thread has 18 threads per inch.

Both the TPI and OD of the thread are required for a positive identification of thread size because more than one size have the same TPI.

Finding correct thread size

Male Threads:
1- Measure the outside diameter (OD) of the large portion of the thread (A).
2- Find the value nearest this dimension in the green columns of chart.
3- The dimension in the yellow column will be your nominal pipe thread size.

Female Threads:
1- Measure top diameter of thread (B)
2- Find the value nearest this dimension in the green columns of chart.
3- The dimension in the yellow column will be your nominal pipe thread size.

AMERICAN NATIONAL STANDARD TAPER PIPE THREAD (NPT)
Nominal pipe size Actual outside diameter (OD) Thread density Thread pitch Effective thread
Length (C) Turns Diameter
inch inch mm inch inch mm inch inch
1/8 0.405 10.287 27 0.03703704 0.9407 0.2639 7.13 0.38000
​1/4 0.540 13.716 18 0.05555555 1.4111 0.4018 7.23 0.50250
3/8 0.675 17.145 18 0.05555555 1.4111 0.4078 7.34 0.63750
​1/2 0.840 21.3360 14 0.07142857 1.8143 0.5337 7.47 0.79178
​3/4 1.050 26.6700 14 0.07142857 1.8143 0.5457 7.64 1.00178
1 1.315 33.4010 ​11 1⁄2 0.08695652 2.2087 0.6828 7.85 1.25631