NPT Threads - Taps and Drill Sizes
NPT - Briggs Standard Pipe threads - Taps and Drill Sizes.
The NPT - National Pipe Taper Threads - is based on the Briggs Standard Pipe Thread.
Drill sizes for Briggs Standard Pipe taps for direct tapping without reaming are indicated below:
| Size Taps (inches) | TPI | Size Drill (inches) |
|---|---|---|
| 1/8 | 27 | 21/64 |
| 1/4 | 18 | 27/64 |
| 3/8 | 18 | 9/16 |
| 1/2 | 14 | 11/16 |
| 3/4 | 14 | 29/32 |
| 1 | 11.5 | 1 1/8 |
| 1 1/4 | 11.5 | 1 15/32 |
| 1 1/2 | 11.5 | 1 23/32 |
| 2 | 11.5 | 2 3/16 |
| 2 1/2 | 8 | 2 9/16 |
| 3 | 8 | 3 3/16 |
| 3 1/2 | 8 | 3 11/16 |
| 4 | 8 | 4 3/16 |
- TPI = threads per inch
- 1 inch = 25.4 mm
