1/8 NPT tap drill size
Letter Q
- Inches
- 0.3320
- Millimetres
- 8.43
- Threads per inch
- 27
Drill a Letter Q hole, then cut the 1/8 NPT thread with a taper pipe tap. This is the size for drilling and tapping with no reamer step.
Charts differ on pipe threads. Some list a smaller drill because they assume the hole is taper-reamed first. If you ream, use the drill size your tap or reamer maker lists.
Many shop charts list Letter R (0.339 in) for 1/8 NPT. Both sizes are in common use; Letter Q leaves slightly more thread.
1/8 NPT thread and hole sizes
| Thread | 1/8 NPT National Pipe Taper, 27 threads per inch |
|---|---|
| Tap drill, no reamer | Letter Q 0.3320 in, 8.43 mm |
| Pitch | 0.0370 in 0.941 mm |
Tools for this job
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