1/4 NPT Tap Drill Size and Pipe Thread Bit
Use a 7/16 drill bit
1/4-18 NPT · 0.4375 in / 11.11 mm · pipe taper
1/4 NPT is a tapered pipe thread for plumbing and fittings. The drill is 7/16 in, sized to the pipe taper.
At a glance
| Tap drill | 7/16 |
|---|---|
| Inches | 0.4375 in |
| Millimetres | 11.11 mm |
| Threads per inch | 18 |
Why this size
NPT is a taper pipe thread. The drill is sized to the pipe minor diameter at the gauge plane. Tap drill: 7/16 (0.4375 in / 11.11 mm).
NPT is a taper thread, not a percent-engagement fit. 7/16 in is the correct tap drill for 1/4 NPT.
Related sizes
Compare with adjacent threads – coarse, fine and the opposite measurement system: