Pipe and Hydraulic Thread Guide: NPT, BSPP, BSPT, JIC, ORFS and SAE Compared
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Most connection failures are identification failures. Two fittings thread together, hold for a while, then weep — because a 37° cone was pushed into a 45° seat, or a 55° British taper was forced into a 60° American one.
This is a plain guide to the thread and seal types you will actually meet on a shop floor, what each one seals on, and which pairs are dangerous because they almost fit.
The quick table
| Type | Thread form | Where it seals | Sealant? | Typical use |
|---|---|---|---|---|
| NPT | Tapered, 60° | On the threads | Yes — tape or dope | General US pipe, air, water, gas |
| NPTF | Tapered, 60° (dryseal) | Thread crest/root interference | No | Hydraulics, fuel |
| NPS / NPSM | Straight, 60° | Gasket or O-ring | No | Mechanical joints, swivels |
| BSPT | Tapered, 55° | On the threads | Yes | UK, EU, Asia pipe |
| BSPP | Straight, 55° | Bonded washer or O-ring | No | UK, EU, Asia hydraulics |
| JIC 37° | Straight UN/UNF | 37° flare cone | No | Hydraulics, high pressure |
| SAE 45° | Straight UN/UNF | 45° flare cone | No | Refrigeration, auto, low pressure |
| SAE ORB | Straight UN/UNF | O-ring on a boss face | No | Pump and valve ports |
| ORFS | Straight UN/UNF | O-ring in a flat face | No | Hydraulics, vibration-heavy |
| Metric | Straight or tapered, 60° | Cone or O-ring | Varies | European equipment |
The three mix-ups that cause most leaks
1. NPT and BSPT
Both are tapered. Both look like ordinary pipe thread. NPT is a 60° thread angle, BSPT is 55°, and the pitches differ at most sizes.
A BSPT male will start into an NPT female and feel fine for two or three turns. It will tighten. It will hold pressure on a bench test. Then it weeps in service, because only a fraction of the thread flank is actually in contact.
The exception that fools people: 1/2" and 3/4" NPT and BSPT share the same threads-per-inch. Those two sizes assemble more convincingly than any other and fail just the same.
2. JIC 37° and SAE 45°
The most common hydraulic mistake there is. Both are straight threads with a flared cone, and in several sizes the threads are identical — only the cone angle differs by eight degrees.
They will thread together completely and torque up. The seal is then a line contact instead of a face contact, which holds at low pressure and fails under a pressure spike.
How to tell them apart: JIC is the standard on industrial hydraulics and is usually steel. SAE 45° turns up on refrigeration, automotive brake and fuel lines, and is often brass. If you are unsure, measure the cone — a 37° seat is visibly shallower than a 45°.
3. ORB and ORFS
Both are straight-thread O-ring seals, and the names get used loosely.
- ORB — the O-ring sits on the threaded end and seals against a machined boss face as you tighten. Port connections on pumps and valves.
- ORFS — the O-ring sits in a groove on a flat face, and a nut squeezes the two faces together. Best vibration resistance of anything on this list.
If the equipment lives on something that shakes, ORFS is the one you want.
Tapered vs. straight — the distinction that explains the rest
Tapered threads (NPT, NPTF, BSPT) seal by wedging. Metal deforms against metal as you tighten, and the seal is the thread. That is why they need tape or dope, and why over-tightening splits female fittings.
Straight threads (NPS, BSPP, JIC, SAE, ORB, ORFS) do not seal on the thread at all. The thread is only a clamp. The seal is a cone, an O-ring or a washer. Putting tape on a straight thread does nothing useful and can hold the sealing faces apart.
Work out which family you are holding first. Everything else follows from that.
Identifying a fitting you have in your hand
- Tapered or straight? Lay a straightedge along the threads. Visible taper means NPT, NPTF or BSPT.
- Measure the OD of the male thread with calipers. Do not trust the nominal size — 1/2" NPT measures about 0.840".
- Check the pitch with a thread gauge. This is what separates NPT from BSPT.
- Look at the seat. A cone means JIC or SAE. A flat face with a groove means ORFS. An O-ring at the base of a straight thread means ORB. A flat with a bonded washer means BSPP.
- Measure the cone angle if there is one. 37° is JIC, 45° is SAE.
A thread pitch gauge and a set of calipers settle almost every argument about this, and both are cheap.
Pressure, briefly
Pressure rating is set by the whole assembly, not the thread type, but the ranking generally runs: ORFS and JIC at the top for hydraulics, NPTF solid for medium-high, NPT fine for air, water and gas at ordinary line pressure, SAE 45° for low pressure, and BSPP with a bonded seal comparable to JIC when it is assembled correctly.
Cycling matters more than the peak number. A joint that sees pressure spikes wants an O-ring seal, not a thread seal.
When you have to cross between standards
Do not force it. Use an adapter. NPT to BSPP, JIC to ORFS, metric to JIC — adapters exist for all of it and cost far less than the downtime from a joint that lets go.
And do not rely on a fitting that "went in fine." On this list, threading together fully is not evidence of a match.
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