| Tap Drills for Pipe Taps Chart |
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| - | American Standard | British Standard | |||
| Nominal OD |
Threads per inch |
NPT | NPS | Threads per inch |
Drill size |
| 1/16 | 27 | D | 1/4 | 28 | G |
| 1/8 | 27 | R | S | 28 | 11/32 |
| 1/4 | 18 | 7/16 | 29/64 | 19 | 15/32 |
| 3/8 | 18 | 37/64 | 19/32 | 19 | 39/64 |
| 1/2 | 14 | 23/32 | 47/64 | 14 | 3/4 |
| 5/8 | - | - | - | 14 | 53/64 |
| 3/4 | 14 | 59/64 | 15/16 | 14 | 31/32 |
| 7/8 | - | - | - | 14 | 1-7/64 |
| 1 | 11.5 | 1-5/32 | 1-3/16 | 11 | 1-7/32 |