NPSL – Loose-Fitting Mechanical Joints With locknuts
The NPSL (Defined in ASTM B1.20) thread series is designed to produce a pipe thread with the largest diameter possible to cut on a standard pipe. The internal and external thread dimensions are designed to have a “loose fit”, and a locknut with an O-ring is required to create a seal.
The “classic” application for the NPSM thread is connecting a pipe to a tank. The seal is achieved with two locknuts with O-rings—one on the inner face of the tank’s wall and the other on the outer face.
NPSL External Thread Dimensions Chart
| Thread | Pipe OD | TPI | Pitch Diameter | Max Major Diameter |
|---|---|---|---|---|
| 1/8-27 NPSL | 0.405 | 27 | 0.384 - 0.3805 | 0.409 |
| 1/4-18 NPSL | 0.54 | 18 | 0.5038 - 0.4986 | 0.541 |
| 3/8-18 NPSL | 0.675 | 18 | 0.6409 - 0.6357 | 0.678 |
| 1/2-14 NPSL | 0.84 | 14 | 0.7963 - 0.7896 | 0.844 |
| 3/4-14 NPSL | 1.05 | 14 | 1.0067 - 1.000 | 1.054 |
| 1-11.5 NPSL | 1.315 | 11.5 | 1.2604 - 1.2523 | 1.318 |
| 1 1/4-11.5 NPSL | 1.66 | 11.5 | 1.6051 - 1.597 | 1.663 |
| 1 1/2-11.5 NPSL | 1.9 | 11.5 | 1.8441 - 1.836 | 1.902 |
| 2-11.5 NPSL | 2.375 | 11.5 | 2.318 - 2.3099 | 2.376 |
| 2 1/2-8 NPSL | 2.875 | 8 | 2.7934 - 2.7817 | 2.877 |
| 3-8 NPSL | 3.5 | 8 | 3.4198 - 3.4081 | 3.503 |
| 3 1/2-8 NPSL | 4 | 8 | 3.9201 - 3.9084 | 4.003 |
| 4-8 NPSL | 4.5 | 8 | 4.4184 - 4.4067 | 4.502 |
| 5-8 NPSL | 5.563 | 8 | 5.4805 - 5.4688 | 5.564 |
| 6-8 NPSL | 6.625 | 8 | 6.5372 - 6.5255 | 6.62 |
| 8-8 NPSL | 8.625 | 8 | 8.5313 - 8.5196 | 8.615 |
| 10-8 NPSL | 10.750 | 8 | 10.6522 - 10.6405 | 10.735 |
| 12-8 NPSL | 12.750 | 8 | 12.6491 - 12.6374 | 12.732 |
NPSL Internal Thread Dimensions Chart
| Thread | TPI | Pitch Diameter | Min Minor Diameter |
|---|---|---|---|
| 1/8-27 NPSL | 27 | 0.3863 - 0.3898 | 0.362 |
| 1/4-18 NPSL | 18 | 0.5073 - 0.5125 | 0.47 |
| 3/8-18 NPSL | 18 | 0.6444 - 0.6496 | 0.607 |
| 1/2-14 NPSL | 14 | 0.8008 - 0.8075 | 0.753 |
| 3/4-14 NPSL | 14 | 1.0112 - 1.0179 | 0.964 |
| 1-11.5 NPSL | 11.5 | 1.2658 - 1.2739 | 1.208 |
| 1 1/4-11.5 NPSL | 11.5 | 1.6106 - 1.6187 | 1.553 |
| 1 1/2-11.5 NPSL | 11.5 | 1.8495 - 1.8576 | 1.792 |
| 2-11.5 NPSL | 11.5 | 2.3234 - 2.3315 | 2.265 |
| 2 1/2-8 NPSL | 8 | 2.8012 - 2.8129 | 2.718 |
| 3-8 NPSL | 8 | 3.4276 - 3.4393 | 3.3114 |
| 3 1/2-8 NPSL | 8 | 3.9279 - 3.9396 | 3.845 |
| 4-8 NPSL | 8 | 4.4262 - 4.4379 | 4.343 |
| 5-8 NPSL | 8 | 5.4884 - 5.5001 | 5.405 |
| 6-8 NPSL | 8 | 6.545 - 6.5567 | 6.462 |
| 8-8 NPSL | 8 | 8.5391 - 8.5508 | 8.456 |
| 10-8 NPSL | 8 | 10.66 - 10.6717 | 10.577 |
| 12-8 NPSL | 8 | 12.6569 - 12.6686 | 12.574 |
