Quick reference for identifying threads in the field. Not a textbook, a working guide built for technicians, mechanics, and engineers who need to make the right call fast.
Never force a fitting. If it doesn't thread smoothly by hand for at least 2–3 turns, stop immediately, you have the wrong thread type, wrong size, or damaged threads. Forcing a mismatched fitting cross-threads the connection, damages both components, and creates a permanent leak path that cannot be fixed by retorquing.
All hydraulic thread types belong to one of three families. Knowing the family tells you which standards to look up.
Thread standards in this family
NPT / NPTF
Tapered pipe thread, 60°, thread-interference seal. Dominant in North American plumbing and low-pressure hydraulics.
JIC
37° flare, straight UNF thread. The standard for industrial hydraulics across North America.
ORFS
O-ring face seal, flat face, straight UNF. Preferred for new mobile equipment builds.
SAE ORB
O-ring boss, straight UNF. The dominant port thread on hydraulic components in North America.
Thread standards in this family
DIN / ISO 6149
Metric straight thread (e.g., M12×1.5). Common on European-manufactured hydraulic components.
BSPP
55° parallel British pipe thread. Widely used in European and Asian equipment ports. Not interchangeable with NPT.
BSPT
55° tapered British pipe thread. Same taper as NPT but incompatible thread angle. Common in Asia.
Thread standards in this family
NPTF (Dryseal)
A precision version of NPT designed to seal without sealant. Used in fuel systems and critical applications.
UN / UNF
Straight thread used as the thread form for JIC, ORFS, and SAE ORB, not a seal thread itself.
SAE J476 (Flare)
45° flare fitting used in some fuel and refrigeration systems. Not the same as JIC 37°.
Print this table and keep it on the service truck. One table, all major thread types.
| Thread | Angle | Taper? | Seal Method | Where You'll See It |
|---|---|---|---|---|
| NPT | 60° | Yes (1:16) | Thread interference | North American plumbing, low-pressure hydraulics, air lines |
| NPTF | 60° | Yes (1:16) | Thread interference (precision) | Fuel systems, higher-pressure pipe connections |
| BSPT | 55° | Yes (1:16) | Thread interference | European/British/Australian equipment, import machinery |
| BSPP | 55° | No (parallel) | Bonded seal / O-ring face | European hydraulic ports, Japanese and Korean equipment |
| JIC | 60° | No (straight UNF) | 37° flare metal-to-metal | Industrial hydraulics, fuel lines, North American equipment |
| ORFS | 60° | No (straight UNF) | O-ring on flat face | Mobile equipment, high-vibration, zero-leak applications |
| SAE ORB | N/A | No (straight UNF) | O-ring on male thread body | Hydraulic ports: pumps, motors, valves, cylinders |
| Metric DIN | 60° | No (straight metric) | O-ring or bonded seal | European hydraulic systems, Bosch Rexroth, Parker European |
NPT and BSPT threads look nearly identical. They have the same nominal sizes (1/4", 1/2", 3/4"...), similar taper rates, and they will often partially thread into each other. This is why they are the most frequently confused thread types, and why mixing them causes leaks that are hard to diagnose.
The Definitive Field Test
Use a thread angle gauge. Or: if the fitting is from North American equipment, it's NPT. If it's from European, Japanese, Korean, or Australian equipment, suspect BSP. When in doubt, bring it to us, we'll confirm it in 30 seconds.
The same thread size can appear in two completely different roles. Confusing port and inline threads leads to wrong fitting orders.
Port threads are machined into the body of a component, a pump, motor, valve, cylinder, or manifold. The fitting threads into the port and the O-ring or seal face makes contact with the machined surface around the port opening.
Inline threads are on fittings that connect two hoses, hose-to-tube, or tube-to-tube. The male end of one fitting mates with the female end of another fitting, no machined port involved. The connection is made between two fitting ends.
How each thread type achieves its seal, and how reliable it is under vibration and pressure cycling.
| Thread Type | Seal Method | Notes | Leak Reliability | Vibration Rating |
|---|---|---|---|---|
| NPT | Thread Interference | Tapered threads wedge together. Sealant (PTFE tape) often added. | Moderate | Poor |
| BSPT | Thread Interference | Same principle as NPT but 55°. Bonded seal can be added. | Moderate | Poor |
| BSPP | Bonded Seal / O-Ring | Flat face seal under hex; O-ring groove at face. Very common in European ports. | Good | Good |
| JIC | 37° Metal-to-Metal Flare | Conical seat contact. No elastomer. Precision flare required. | Good | Fair |
| ORFS | O-Ring on Flat Face | O-ring in machined groove. Best available seal for inline connections. | Excellent | Excellent |
| SAE ORB | O-Ring on Thread Body | O-ring on male fitting OD seals against port face on installation. | Excellent | Excellent |
| Metric DIN | O-Ring / Bonded Seal | Various, confirm by looking for O-ring groove or bonded seal recess. | Good–Excellent | Good |
When you're standing in the field with an unknown fitting in hand, run through these three questions in order. Most fittings are identified by question two.
Run your fingertip along the thread from tip to base. Does the diameter change? If yes (tapered): you have NPT, BSPT, or possibly NPTF. If no (parallel, constant diameter): you have BSPP, JIC, ORFS, SAE ORB, or metric. This one question eliminates half the thread types immediately.
Look at the end face and thread body of the fitting. Flat face with O-ring groove = ORFS. 37° inner cone visible = JIC. O-ring sitting around the thread body (on the male) = SAE ORB. Flat face with no groove (for a bonded seal) = BSPP. Tapered with no special interface = NPT or BSPT. This is usually the deciding question.
If you've reached this question, you're distinguishing between NPT (60°) and BSPT (55°). Use a thread angle gauge if available. If not, consider the equipment origin: North American = NPT, British/European/Australian/Asian import = BSP. When stakes are high and you can't confirm, call us, we'll identify it in seconds.
Bring any fitting to our Cleveland, TN location. Our specialists will identify the thread type, seal method, and size, and pull the correct replacement from stock.
Deep dive on the two most common fitting types.
Dash sizes, flow rates, and pressure ratings.
Causes, risks, and proven fixes.
The 6-step process to ID any fitting.