NPT THREAD CHART



NPT Thread Chart for basic dimensions of general purpose NPT pipe threads (inch) according to ANSI/ASME B1.20.1-1983 standard.

- NPT Thread taper angle = 1/16 taper = 1 deg. 47 min = 0.75 in./ft .

- The angle between the sides of the thread is 60 deg.

- Thread Designation: The nominal pipe size, number of threads per inch and the thread series symbol in sequence. Ex: 3/8 - 18 NPT

- See NPT Pipe Thread Calculator for calculator form of the NPT thread chart.

NPT Thread Chart
American National Standard Taper Pipe Thread (NPT)

Nom. Pipe Size Outer Dia. of Pipe TPI Pitch of Thread Ptich Dia. at Begining of External Thread Handtight Engagement Effective Thread, External Overall Length, External Thread (L4) b Basic Minor Dia. at Small End of Pipe a
Length (L1) Dia.
(E1)
Length (L2) Dia. (E2)
inch Thd. inch Thd.
1/16 0.3125 27 0.03704 0.27118 0.160 4.32 0.28118 0.2611 7.05 0.28750 0.3896 0.2416
1/8 0.405 27 0.03704 0.36351 0.1615 4.36 0.37360 0.2639 7.12 0.38000 0.3924 0.3339
1/4 0.540 18 0.05556 0.47739 0.2278 4.10 0.49163 0.4018 7.23 0.50250 0.5946 0.4329
3/8 0.675 18 0.05556 0.61201 0.240 4.32 0.62701 0.4078 7.34 0.63750 0.6006 0.5676
1/2 0.840 14 0.07143 0.75843 0.320 4.48 0.77843 0.5337 7.47 0.79179 0.7815 0.7013
3/4 1.050 14 0.07143 0.96768 0.339 4.75 0.98887 0.5457 7.64 1.00179 0.7935 0.9105
1 1.315 11.5 0.08696 1.21363 0.400 4.60 1.23863 0.6828 7.85 1.25630 0.9845 1.1441
1 1/4 1.660 11.5 0.08686 1.55713 0.420 4.83 1.58338 0.7068 8.13 1.60130 1.0085 1.4876
1 1/2 1.900 11.5 0.08696 1.79609 0.420 4.83 1.82234 0.7235 8.32 1.84130 1.0252 1.7265
2 2.375 11.5 0.08696 2.26902 0.436 5.01 2.29627 0.7565 8.70 2.31630 1.0582 2.1995
2 1/2 2.875 8 0.12500 2.71953 0.682 5.46 2.76216 1.1375 9.10 2.79062 1.5712 2.6195
3 3.500 8 0.12500 3.34062 0.766 6.13 3.38850 1.20000 9.60 3.41562 1.6337 3.2406
3 1/2 4.000 8 0.12500 3.83750 0.821 6.57 3.88881 1.2500 10.00 3.91562 1.6837 3.7375
4 4.5000 8 0.12500 4.33438 0.844 6.75 4.38712 1.3000 10.40 4.41562 1.7337 4.2344
5 5.563 8 0.12500 5.39073 0.937 7.50 5.44929 1.4063 11.25 5.47862 1.8400 5.2907
6 6.625 8 0.12500 6.44609 0.958 7.66 6.50597 1.5125 12.10 6.54062 1.9462 6.3461
8 8.625 8 0.12500 8.43359 1.063 8.50 8.50003 1.7125 13.70 8.54062 2.1462 8.3336
10 10.750 8 0.12500 10.54531 1.210 9.68 10.62094 1.9250 15.40 10.66562 2.3587 10.4453
12 12.750 8 0.12500 12.53281 1.360 10.88 12.61781 2.1250 17.00 12.66562 2.5587 12.4328
14 O.D. 14.000 8 0.12500 13.77500 1.562 12.50 13.87262 2.2500 18.00 13.91562 2.6837 13.6750
16 O.D. 16.000 8 0.12500 15.76250 1.812 14.50 15.87575 2.4500 19.60 15.91562 2.8837 15.6625
18 O.D. 18.000 8 0.12500 17.75000 2.000 16.00 17.87500 2.6500 21.20 17.91562 3.0837 17.6500
20 O.D. 20.000 8 0.12500 19.73750 2.125 17.00 19.87031 2.8500 22.80 19.91562 3.2837 19.6375
24 O.D. 24.000 8 0.12500 23.71250 2.375 19.00 23.86094 3.2500 26.00 23.91562 3.6837 23.6125

Note: The dimensions of the NPT Thread are given to four or five decimal places. While this implies a greater degree of precision than is ordinarily achieved, these dimensions are the basis of gage dimensions and are so expressed for the purpose of eliminating errors in computations.

Notea: Given as information for use in selecting tap drills. See Drill Sizes for NPT Pipe Threads Calculator.

Noteb: Reference dimension.

Note: For additional dimensions, see NPT Pipe Thread Calculator.


Definitions:

NPT: National Pipe Thread Taper

Reference:

  • ANSI/ASME B1.20.1 - 1983 Pipe Threads, General Purpose (Inch)
  • Oberg, E. , Jones ,F.D. , Horton H.L. , Ryffel H.H., (2016) . Machinery's Handbook . 30th edition.  Industrial Press Inc.
  • Oberg, E. , Jones ,F.D. , Horton H.L. , Ryffel H.H., (2012) . Machinery's Handbook . 29th edition.  Industrial Press Inc. , pp 1956 - 1965