Shop reference tools
NPT Tap Drill Chart
Quick reference for common NPT pipe tap drill sizes.
NPT Tap Drill Chart lookup
Start with the table, then use the related pages for tapping, clearance holes, pilot holes, and printable shop sheets.
| NPT size | Suggested drill | Decimal inch | Millimeters |
|---|---|---|---|
| 1/8-27 NPT | R | 0.339 in | 8.61 mm |
| 1/4-18 NPT | 7/16 in | 0.438 in | 11.11 mm |
| 3/8-18 NPT | 37/64 in | 0.578 in | 14.68 mm |
| 1/2-14 NPT | 23/32 in | 0.719 in | 18.26 mm |
| 3/4-14 NPT | 59/64 in | 0.922 in | 23.42 mm |