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 |