F.A.Q Frequently Asked Questions
What does National Pipe Thread (NPT) mean?
National Pipe Threads (NPT) Explained
Male threads:Measure the outside diameter of the large portion of the thread at “A“; Find figure nearest this dimension in column 1 or 2 of chart. The dimension in column 3 will be your nominal pipe thread size.
Female Threads:Measure top diameter of thread at “B“; Find figure nearest this dimension in column 1 or 2 of chart. The dimension in column 3 will be your nominal pipe thread size.
| Column 1 | Column 2 | Column 3 | Column 4 | Column 5 | Column 6 |
| OD Fraction Inch (quick reference only) |
OD Actual (inches) |
Pipe Thread Size |
Normal engagement for tight joint (dimension “C“) |
Threads per Inch |
Circumference (inches) |
| 5/16 | 0.3125 |
1/16
|
0.2611 | 27 | 0.9817 |
| 13/32 | 0.405 |
1/8
|
0.2639 | 27 | 1.272 |
| 35/64 | 0.540 |
1/4
|
0.4018 | 18 | 1.696 |
| 43/64 | 0.675 |
3/8
|
0.4078 | 18 | 2.121 |
| 27/32 | 0.840 |
1/2
|
0.5337 | 14 | 2.639 |
| 1-3/64 | 1.050 |
3/4
|
0.5457 | 14 | 3.299 |
| 1-5/16 | 1.315 |
1
|
0.6828 | 11-1/2 | 4.131 |
| 1-21/32 | 1.660 |
1-1/4
|
0.7068 | 11-1/2 | 5.215 |
| 1-29/32 | 1.900 |
1-1/2
|
0.7235 | 11-1/2 | 5.969 |
| 2-3/8 | 2.375 |
2
|
0.7565 | 11-1/2 | 7.461 |
| 2-7/8 | 2.875 |
2-1/2
|
1.1375 | 8 | 9.032 |
| 3-1/2 | 3.5 |
3
|
1.2000 | 8 | 10.995 |
| 4 | 4.0 |
3-1/2
|
1.2500 | 8 | 12.566 |
| 4-1/2 | 4.5 |
4
|
1.3000 | 8 | 14.137 |
| 5-5/8 | 5.563 |
5
|
1.4063 | 8 | 17.476 |
| 6-5/8 | 6.625 |
6
|
1.5125 | 8 | 20.812 |
| 8-5/8 | 8.625 |
8
|
1.7125 | 8 | 27.095 |
| 10-3/4 | 10.75 |
10
|
1.9250 | 8 | 33.771 |
| 12-3/4 | 12.75 |
12
|
2.1250 | 8 | 40.054 |
