What is a Pipe Thread?
The American National Standard Pipe Thread Standard, usually referred to as the National Pipe Thread Standard, is a thread structure with a specific tooth shape. It is a standardized thread used for pipe connections to achieve sealing and fixation between pipes, valves, and pipe fittings.
Types of pipe threads
- NPT or NPS (National Standard Tapered Pipe or Straight Pipe): The most common pipe in North America, covering fields such as petrochemicals.
- MIP or FIP (External or Internal Threaded Iron Pipe): The common name for NPT threads, specifically referring to cast iron pipes. The size standard is the same as NPT, but the material is emphasized to be cast iron.
- BSP(T) or BSP(S) (British Standard Tapered Pipe or Straight Pipe): The most common in Europe, BSPT (R thread) is a 55° tooth angle, 1:16 taper, self-sealing design, and meets ISO 7 standards. BSPP (G thread), straight pipe thread, requires gasket sealing, standard is ISO 228
- Compression: A unique threaded joint with a double ferrule design, which squeezes the ferrule into the pipe to form a seal through the nut, without welding and tape.
- UNS (Uniform Special Thread): A customized thread standard that meets high temperature, strong corrosion and other environments, partially compatible with compression joints.
Pipe thread standard sizes
NSI B1.20.1 -npt pipe thread dimensions American national standard taper pipe thread
pipe thread dimensions chart
|
Nominal |
Thread |
Thread pitch P |
Hand-tight engagement |
Effective thread |
Overall |
Actual outside |
Tap drill |
|||||||
|
Length L1 |
Turns |
Diameter E1 |
Length L2 |
Turns |
Diameter E2 |
|||||||||
|
inch |
inch−1 |
inch |
mm |
inch |
inch |
inch |
inch |
inch |
inch |
mm |
inch |
mm |
||
|
1⁄16 |
27 |
0.03703704 |
0.9407 |
0.1600 |
4.32 |
0.28118 |
0.2611 |
7.05 |
0.2875 |
0.3896 |
0.313 |
7.950 |
||
|
1⁄8 |
27 |
0.03703704 |
0.9407 |
0.1615 |
4.36 |
0.37360 |
0.2639 |
7.13 |
0.38000 |
0.3924 |
0.405 |
10.287 |
0.339 |
8.6106 |
|
1⁄4 |
18 |
0.05555555 |
1.4111 |
0.2278 |
4.10 |
0.49163 |
0.4018 |
7.23 |
0.50250 |
0.5946 |
0.540 |
13.716 |
7⁄16 |
11.113 |
|
3⁄8 |
18 |
0.05555555 |
1.4111 |
0.2400 |
4.32 |
0.62701 |
0.4078 |
7.34 |
0.63750 |
0.6006 |
0.675 |
17.145 |
37⁄64 |
14.684 |
|
1⁄2 |
14 |
0.07142857 |
1.8143 |
0.3200 |
4.48 |
0.77843 |
0.5337 |
7.47 |
0.79178 |
0.7815 |
0.840 |
21.3360 |
23⁄32 |
18.2563 |
|
3⁄4 |
14 |
0.07142857 |
1.8143 |
0.3390 |
4.75 |
0.98887 |
0.5457 |
7.64 |
1.00178 |
0.7935 |
1.050 |
26.6700 |
59⁄64 |
23.4156 |
|
1 |
11+1⁄2 |
0.08695652 |
2.2087 |
0.4000 |
4.60 |
1.23863 |
0.6828 |
7.85 |
1.25631 |
0.9845 |
1.315 |
33.4010 |
1+5⁄32 |
29.3688 |
|
1+1⁄4 |
11+1⁄2 |
0.08695652 |
2.2087 |
0.4200 |
4.83 |
1.58338 |
0.7068 |
8.13 |
1.60131 |
1.0085 |
1.660 |
42.1640 |
1+1⁄2 |
38.1000 |
|
1+1⁄2 |
11+1⁄2 |
0.08695652 |
2.2087 |
0.4200 |
4.83 |
1.82234 |
0.7235 |
8.32 |
1.84131 |
1.0252 |
1.900 |
48.2600 |
1+47⁄64 |
44.0531 |
|
2 |
11+1⁄2 |
0.08695652 |
2.2087 |
0.4360 |
5.01 |
2.29627 |
0.7565 |
8.70 |
2.31630 |
1.0582 |
2.375 |
60.3250 |
2+7⁄32 |
56.3563 |
|
2+1⁄2 |
8 |
0.12500000 |
3.1750 |
0.6820 |
5.46 |
2.76216 |
1.1375 |
9.10 |
2.79063 |
1.5712 |
2.875 |
73.0250 |
2+5⁄8 |
66.6750 |
|
3 |
8 |
0.12500000 |
3.1750 |
0.7660 |
6.13 |
3.38850 |
1.2000 |
9.60 |
3.41563 |
1.6337 |
3.500 |
88.9000 |
3+1⁄4 |
82.5500 |
|
3+1⁄2 |
8 |
0.12500000 |
3.1750 |
0.8210 |
6.57 |
3.88881 |
1.2500 |
10.00 |
3.91563 |
1.6837 |
4.000 |
101.6000 |
3+3⁄4 |
95.2500 |
|
4 |
8 |
0.12500000 |
3.1750 |
0.8440 |
6.75 |
4.38713 |
1.3000 |
10.40 |
4.41563 |
1.7337 |
4.500 |
114.3000 |
4+1⁄4 |
107.9500 |
|
4+1⁄2 |
8 |
0.12500000 |
3.1750 |
5.000 |
127.0000 |
4+3⁄4 |
120.6500 |
|||||||
|
5 |
8 |
0.12500000 |
3.1750 |
0.9370 |
7.50 |
5.44929 |
1.4063 |
11.25 |
5.47863 |
1.8400 |
5.563 |
141.3002 |
5+9⁄32 |
134.1438 |
|
6 |
8 |
0.12500000 |
3.1750 |
0.9580 |
7.66 |
6.50597 |
1.5125 |
12.10 |
6.54063 |
1.9462 |
6.625 |
168.2750 |
6+11⁄32 |
161.1313 |
|
8 |
8 |
0.12500000 |
3.1750 |
1.0630 |
8.50 |
8.50003 |
1.7125 |
13.70 |
8.54063 |
2.1462 |
8.625 |
219.0750 |
||
|
10 |
8 |
0.12500000 |
3.1750 |
1.2100 |
9.68 |
10.62094 |
1.9250 |
15.40 |
10.66563 |
2.3587 |
10.750 |
273.0500 |
||
|
12 |
8 |
0.12500000 |
3.1750 |
1.3600 |
10.88 |
12.61781 |
2.1250 |
17.00 |
12.66563 |
2.5587 |
12.750 |
323.8500 |
||
|
14 |
8 |
0.12500000 |
3.1750 |
1.5620 |
12.50 |
13.87263 |
2.2500 |
18.00 |
13.91563 |
2.6837 |
14.000 |
355.6000 |
||
|
16 |
8 |
0.12500000 |
3.1750 |
1.8120 |
14.50 |
15.87575 |
2.4500 |
19.60 |
15.91563 |
2.8837 |
16.000 |
406.4000 |
||
|
18 |
8 |
0.12500000 |
3.1750 |
2.0000 |
16.00 |
17.87500 |
2.6500 |
21.20 |
17.91563 |
3.0837 |
18.000 |
457.2000 |
||
|
20 |
8 |
0.12500000 |
3.1750 |
2.1250 |
17.00 |
19.87031 |
2.8500 |
22.80 |
19.91563 |
3.2837 |
20.000 |
508.0000 |
||
|
24 |
8 |
0.12500000 |
3.1750 |
2.3750 |
19.00 |
23.86094 |
3.2500 |
26.00 |
23.91563 |
3.6837 |
24.000 |
609.6000 |
||
NOTE!
Pipe size does not refer to any physical dimensions. The outside diameter of the pipe or fitting must be measured and compared to the table to determine the size
NPT threads are not interchangeable with NPS (National Pipe Parallel Thread).
NPT threads are similar in appearance to ISO 7-1 threads. However, ISO and NPT threads should not be mixed.
FAQs
1. Why are NPT threads not interchangeable with NPS (National Pipe Straight Thread)?
NPT and NPS threads have the same thread angle of 60°, shape and pitch. However, NPT threads are tapered, while NPS threads are straight threads (parallel).
2. What are the typical markings for NPT threads?
1⁄8 – 27 NPT
3. What are the differences between MIP and FIP?
MIP is the abbreviation for male iron pipe, and FIP is the abbreviation for female iron pipe
