3/4 NPT Tap Drill Size
3/4-14 NPT · American National Standard taper pipe thread · ASME B1.20.1
What size drill bit for a 3/4 NPT tap?
To scale male thread, side section
3/4-14 NPT ASME B1.20.1
| Pipe outside diameter | 1.050 in / 26.67 mm |
|---|---|
| Threads per inch | 14 TPI (pitch 0.0714 in) |
| Taper | 1:16 on diameter |
| Pitch dia at pipe end (E0) | 0.9677 in |
| Pitch dia at L1 (E1) | 0.9889 in |
| Hand-tight engagement (L1) | 0.339 in, 4.75 turns |
| Effective thread (L2) | 0.5457 in |
| Wrench makeup | 0.2143 in, 3 turns |
| Thread height | 0.0571 in |
Shop notes
3/4 NPT has an outside diameter of 1.050 in, over an inch, and takes a 59/64 drill (0.9219 in, 23.4 mm) when you tap it without a reamer. Tapping a straight hole to a full taper means the tap does all the shaping, and at this size that takes real torque. A long tap handle and a part clamped firmly to something solid do more for thread quality than any cutting oil.
It shares 14 TPI and a thread height of 0.0571 in with 1/2 NPT, but it has the longest hand-tight engagement of the sizes here in turns: 0.339 in, about 4.75 turns, before the 3 wrench turns. If a fitting stops well short of that by hand, check the hole for chips or a damaged first thread before forcing it.
Not a garden hose thread
Garden hose thread (GHT) is also called 3/4 in, and that is where the resemblance ends. GHT is a straight thread with a different pitch, and it seals on a rubber washer at the end, not on the flanks. A hose fitting will not make up properly on a 3/4 NPT pipe, and tape will not fix it. Use an adapter made for the job.
NPT itself seals on the thread flanks, so the pipe side needs PTFE tape or a pipe thread sealant.