NPT pipe thread chart
National Pipe Taper threads from 1/16 to 2 inch: threads per inch, the actual pipe outside diameter, and the tap drill to use without reaming. NPT tapers 1 in 16 on diameter (3/4 in per foot).
| Nominal size | TPI | Pipe OD (in) | Tap drill | Decimal (in) |
|---|---|---|---|---|
| 1/16-27 NPT | 27 | 0.313 | D | 0.2460 |
| 1/8-27 NPT | 27 | 0.405 | R | 0.3390 |
| 1/4-18 NPT | 18 | 0.540 | 7/16 | 0.4375 |
| 3/8-18 NPT | 18 | 0.675 | 37/64 | 0.5781 |
| 1/2-14 NPT | 14 | 0.840 | 23/32 | 0.7188 |
| 3/4-14 NPT | 14 | 1.050 | 59/64 | 0.9219 |
| 1-11.5 NPT | 11.5 | 1.315 | 1-5/32 | 1.1563 |
| 1-1/4-11.5 NPT | 11.5 | 1.660 | 1-1/2 | 1.5000 |
| 1-1/2-11.5 NPT | 11.5 | 1.900 | 1-47/64 | 1.7344 |
| 2-11.5 NPT | 11.5 | 2.375 | 2-7/32 | 2.2188 |
Common questions
- What tap drill for 1/4 NPT?
- 7/16 in (0.4375 in) without reaming.
- Why is a 1/2 NPT fitting not 1/2 inch across?
- Pipe sizes are nominal. A 1/2 NPT pipe is 0.840 in in outside diameter.
- What is the NPT taper?
- 1 in 16 on diameter, which is 3/4 in per foot, or 1°47′ per side.