Thread identification
NPT / NPTF Tapered Pipe (SAE J516)
NPT and NPTF are tapered pipe threads that seal on the threads themselves as they wedge together. They're identified by their visible taper and the absence of any cone seat or O-ring, and they remain common on ports, gauges, and older equipment.
Identify it
Four checks at the bench.
- 01
Look for taper: thread OD visibly shrinks toward the end of the fitting
- 02
No seat, no O-ring — the threads are the seal
- 03
Measure nominal size (a '1/2 NPT' measures about 0.84" OD — pipe sizes, not actual OD)
- 04
NPTF (Dryseal) has modified crests for sealing without sealant; in practice most users still apply paste
Don't confuse it with…
- BSPT (British taper) has a 55° flank angle vs NPT's 60° and different pitches at several sizes — they will start together and leak forever
- A tapered fitting forced into a straight (parallel) port cracks castings
Reference
Size chart.
| Size | Thread |
|---|---|
| 1/8" NPT | 27 TPI |
| 1/4" NPT | 18 TPI |
| 3/8" NPT | 18 TPI |
| 1/2" NPT | 14 TPI |
| 3/4" NPT | 14 TPI |
| 1" NPT | 11-1/2 TPI |
A1 stocks it.
- NPTF Male Pipe Hose EndA1-WB-NPTM
- Interlock NPTF MaleA1-4S-NPTM
- JIC ↔ NPT Adapter SeriesA1-FA-JNPT
- BSP ↔ NPT Adapter SeriesA1-FA-BNPT
Unsure even after the checks? Bring the fitting to the counter — gauging an unknown thread takes us about a minute. (817) 589-7101.
NPT / NPTF Tapered Pipe (SAE J516) — FAQs
Should I use PTFE tape on NPT hydraulic fittings?
Use hydraulic-rated paste sealant rather than tape where possible — tape shreds into slivers that end up in valves. Keep the first two threads bare either way.
Why do NPT joints loosen with vibration?
The seal is thread deformation, and vibration works it loose. That's why modern hydraulic design prefers ORB ports and ORFS unions over pipe threads.
Is NPT the same as BSPT?
No — flank angles (60° vs 55°) and several pitches differ. They'll engage a few turns, then leak. Identify before you wrench.