NPT Tap Drills
11 rows
Tap drill sizes for American Standard taper pipe threads (NPT), for holes tapped without a taper reamer. These are starting sizes; production work in one material may justify a different drill.
| Tap | TPI | Tap drill | Diameter (in) |
|---|---|---|---|
| 1/16 NPT | 27 | C | 0.242 |
| 1/8 NPT | 27 | Q | 0.332 |
| 1/4 NPT | 18 | 7/16 | 0.438 |
| 3/8 NPT | 18 | 9/16 | 0.562 |
| 1/2 NPT | 14 | 45/64 | 0.703 |
| 3/4 NPT | 14 | 29/32 | 0.906 |
| 1 NPT | 11-1/2 | 1-9/64 | 1.141 |
| 1-1/4 NPT | 11-1/2 | 1-31/64 | 1.484 |
| 1-1/2 NPT | 11-1/2 | 1-47/64 | 1.734 |
| 2 NPT | 11-1/2 | 2-7/32 | 2.219 |
| 2-1/2 NPT | 8 | 2-5/8 | 2.625 |
Based on NBS Handbook H28 (1957), Part II, Table 7.2