National Standard Taper Pipe Threads Size NPT Chart

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Manufacturing Processes | Applications and Design

National Standard Taper Pipe Threads Size NPT Chart - Includes both External and internal Pipe Thread Data. The taper rate for all NPT threads is 1⁄16 (3⁄4 inch per foot) measured by the change of diameter (of the pipe thread) over distance. The angle between the taper and the center axis of the pipe is 1° 47'′ 24"″ (1.7899°). Commonly-used sizes are 1/⁄8, 1/⁄4, 3/⁄8, 1⁄/2, 3⁄/4, 1, 1 1⁄/4, 1 1⁄/2, and 2 inch, appearing on pipes and fittings by most U.S. suppliers. Sizes smaller than 1/⁄8 inch are occasionally used for compressed air, while sizes larger than 2 inches are uncommon, due to the use of alternative methods of joining that are used with these larger sizes. NPT is defined by ANSI/ASME standard B1.20.1.

Nominal Pipe Size is loosely related to the inside diameter of Schedule 40 pipe. Because of the pipe wall thickness, the actual diameter of the threads is larger than the NPS, considerably so for small NPS. Other schedules of pipe have different wall thickness but the OD (outer diameter) and thread profile remain the same, so the inside diameter of the pipe is therefore different from the nominal diameter.

Notes:

Outside Diameter D
Nominal Pipe Size
Threads per Inch (Pitch)
Thread Pitch Length, P
Pitch Diameter at External Thread Start E0
Hand Tight Thread Engagement
Length, L1
Diameter E1
Maximum Thread Engagement L2
Diameter E2
0.3125
1⁄16
27
0.03704
0.27118
0.160
0.28118
0.2611
0.28750
0.405
1⁄8
27
0.03704
0.36351
0.1615
0.37360
0.2639
0.38000
0.540
1⁄4
18
0.05556
0.47739
0.2278
0.49163
0.4018
0.50250
0.675
3⁄8
18
0.05556
0.61201
0.240
0.62701
0.4078
0.63750
0.840
1⁄2
14
0.07143
0.75843
0.320
0.77843
0.5337
0.79179
1.050
3⁄4
14
0.07143
0.96768
0.339
0.98887
0.5457
1.00179
1.315
1
11 1⁄2
0.08696
1.21363
0.400
1.23863
0.6828
1.25630
1.660
1 1⁄4
11 1⁄2
0.08696
1.55713
0.420
1.58338
0.7068
1.60130
1.900
1 1⁄2
11 1⁄2
0.08696
1.79609
0.420
1.82234
0.7235
1.84130
2.375
2
11 1⁄2
0.08696
2.26902
0.436
2.29627
0.7565
2.31630
2.875
2 1⁄2
8
0.12500
2.71953
0.682
2.76216
1.1375
2.79062
3.500
3
8
0.12500
3.34062
0.766
3.38850
1.2000
3.41562
4.000
3 1⁄2
8
0.12500
3.83750
0.821
3.88881
1.2500
3.91562
4.500
4
8
0.12500
4.33438
0.844
4.38712
1.3000
4.41562
5.563
5
8
0.12500
5.39073
0.937
5.44929
1.4063
5.47862
6.625
6
8
0.12500
6.44609
0.958
6.50597
1.5125
6.54062
8.625
8
8
0.12500
8.43359
1.063
8.50003
1.7125
8.54062
10.750
10
8
0.12500
10.54531
1.210
10.62094
1.9250
10.66562
12.750
12
8
0.12500
12.53281
1.360
12.61781
2.1250
12.66562
14.000
14
8
0.12500
13.77500
1.562
13.87262
2.2500
13.91562
16.000
16
8
0.12500
15.76250
1.812
15.87575
2.4500
15.91562
18.000
18
8
0.12500
17.75000
2.000
17.87500
2.6500
17.91562
20.000
20
8
0.12500
19.73750
2.125
19.87031
2.8500
19.91562
24.000
24
8
0.12500
23.71250
2.375
23.86094
3.2500
23.91562

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