Standard Pipe Thread Fittings
American Standard Taper Pipe Threads (NPT)
| Nominal size (inside diameter) | Actual OD | Threads per inch | Length of engagement (tightened by hand) | Hand tight turns | Wrench makeup turns | Length of effective thread |
|---|---|---|---|---|---|---|
| 1/16 | 0.3125 | 27 | 0.160 | 0.2611 | ||
| 1⁄8 | 0.405 | 27 | 0.180 | 4½ | 2½ | 0.260 |
| ¼ | 0.540 | 18 | 0.200 | 4 | 3 | 0.401 |
| 3⁄8 | 0.675 | 18 | 0.240 | 4½ | 3 | 0.408 |
| ½ | 0.840 | 14 | 0.320 | 4½ | 3 | 0.534 |
| ¾ | 1.050 | 14 | 0.340 | 4½ | 3 | 0.546 |
| 1 | 1.315 | 11.5 | 0.400 | 4½ | 3¼ | 0.682 |
| 1¼ | 1.660 | 11.5 | 0.420 | 4½ | 3¼ | 0.707 |
| 1½ | 1.900 | 11.5 | 0.420 | 4½ | 3¼ | 0.724 |
| 2 | 2.375 | 11.5 | 0.436 | 5 | 3 | 0.756 |
| 2½ | 2.875 | 8 | 0.682 | 5½ | 3 | 1.136 |
| 3 | 3.500 | 8 | 0.766 | 6 | 3 | 1.2000 |
| 3½ | 4.000 | 8 | 0.821 | 6½ | 3½ | 1.2500 |
| 4 | 4.500 | 8 | 0.844 | 6¾ | 3½ | 1.3000 |
| 5 | 5.563 | 8 | 0.937 | 7½ | 3¾ | 1.4063 |
See below illustrations of (when viewed at 100%).
