3/4" NPT has 14 threads per inch and is cut on pipe 1.050" (26.7 mm) across. A male 3/4" NPT thread measures about 1.043" (26.49 mm) across its tops.
3/4 inch NPT dimensions
| 3/4" NPT | |
|---|---|
| Thread | 3/4-14 NPT |
| Threads per inch | 14 (one thread every 0.0714") |
| Outside of the pipe it’s cut on | 1.050" (26.7 mm) |
| Male thread, measured across | about 1.043" (26.49 mm) |
| Female thread, measured across | about 0.914" (23.21 mm) |
| Taper | 1 in 16 on the diameter (3/4" per foot) |
| Thread angle | 60° |
| Screwed in by hand | 0.339" (4.75 threads) |
| Effective thread length, male end | 0.5457" |
| Overall thread length, male end | 0.7935" |
Pipe outside, taper, angle and lengths: the National Bureau of Standards pipe thread tables (Handbook H28, Table VII.2). Measured diameters: Swagelok’s thread identification guide, which gives them to help identify a thread, not as exact sizes, since every thread has tolerances.
On a tapered thread the reading depends on where you measure, because the male end widens from its tip toward the back. Swagelok’s guide says to measure at the fourth or fifth full thread. By hand, a 3/4" fitting takes up 0.339" of the thread, under half of the 0.7935" cut on the male end.
For 3/4" pipe of every kind, including copper and PEX that aren’t threaded, see 3/4" pipe OD. If you don’t know what thread you have, start at pipe thread size.
What screws onto 3/4 inch NPT
- Water heaters: Rheem says the hot and cold connections on all its models are 3/4" NPT, and A.O. Smith’s residential gas water heater guide calls for 3/4" NPT at the hot and cold nipples, which are steel. See water heater connections.
- Water heater connectors: BrassCraft’s run from a 3/4" FIP nut to the house pipe, with copper sweat, crimp PEX, push or 7/8" compression at the other end.
- Outdoor faucets: Watts makes a hose bibb with a 3/4" male NPT inlet (LFSC8-6) and a lawn faucet with a 3/4" female NPT inlet (LFSC8-4).
- Sprinkler rotors: Rain Bird’s 5000 Series rotors have a 3/4" NPT female bottom inlet. See sprinkler head thread size.
Threads that look like 3/4 inch NPT
- Garden hose thread is about 1.0625" across, a hair wider than 3/4" NPT, but it has 11.5 threads per inch and seals on a washer. A hose needs an adapter: see garden hose to 3/4" pipe and hose thread vs pipe thread.
- 3/4" BSP, the British pipe thread, is about 1.041" (26.44 mm) across with the same 14 threads per inch, but a 55° thread. See BSP vs NPT.
Sealing 3/4 inch NPT
Put PTFE tape or pipe thread sealant on the male thread: NPT makes its seal on the tapered threads. Swagelok calls for 1/2" wide tape at this size. No standard sets a torque or a number of turns once the joint is past hand-tight. Each maker’s wrap count is on threaded fitting leaking.
Shut off the water, and the power or gas to a water heater, before you open a threaded joint. What Adapter For covers water fittings only, not gas lines.