How to Identify Hydraulic Fitting Thread Types: JIC, NPT, ORFS, and BSPP

Mixing thread standards is one of the most common causes of hydraulic leaks. SC Fastening Systems shows you how to tell these fittings apart before you connect them.

A hydraulic connection that looks like it fits and threads together isn’t necessarily correct. Several thread standards share similar sizes and pitch, which means it’s possible to force two incompatible fittings together, get a connection that seems tight, and still end up with a leak — or a failure — under pressure. Knowing how to identify what you’re holding is the first step to sourcing the right replacement or matching an existing system correctly.

JIC (37° Flare)

JIC — Joint Industry Council — fittings are the most common standard in North American hydraulic systems. They seal by metal-to-metal contact on a 37-degree flared cone, with straight threads that don’t seal on their own.

• How to identify it: Look at the end of the male fitting — a visible 37-degree flare with straight threads is the giveaway. The seal happens at the flare face, not the threads.
• Common use: General hydraulic hose and tube assemblies across construction, agriculture, and industrial equipment.

NPT (National Pipe Taper)

NPT fittings seal differently than JIC entirely — the threads themselves are tapered, and the seal comes from the threads wedging together as they’re tightened, usually backed up with thread sealant or tape.

• How to identify it: The threads visibly narrow toward the end of the fitting rather than running straight and parallel. There’s no flare or separate sealing face — the taper is the seal.
• Common use: Pipe connections, ports on pumps and valves, and lower-pressure plumbing-style connections.
• Watch for: NPT and BSPP threads can look deceptively similar at a glance. Forcing an NPT fitting into a BSPP port (or vice versa) can cross-thread the port or leave a connection that never fully seals.

ORFS (O-Ring Face Seal)

ORFS fittings use straight threads for mechanical strength but seal on a flat face, with a captured O-ring doing the actual sealing work rather than the threads or a flare.

• How to identify it: A flat face at the end of the male fitting with a visible O-ring groove, rather than a flared cone. Straight threads with no taper.
• Common use: High-pressure hydraulic systems where a leak-free connection is critical and vibration resistance matters — increasingly the standard for demanding applications over JIC.

BSPP (British Standard Pipe Parallel)

BSPP fittings use straight (parallel) threads, unlike the tapered NPT they’re often mistaken for. Sealing typically happens through a bonded washer or O-ring at the base of the fitting rather than the threads themselves.

• How to identify it: Straight, parallel threads (not tapered like NPT) — often paired with a bonded seal washer visible at the fitting’s shoulder.
• Common use: Equipment built to international or European standards, common on imported machinery and instrumentation.

A Practical Way to Check What You Have

1. Look at the end of the fitting. A flare = JIC. A flat face with an O-ring groove = ORFS. No flare, no groove = likely NPT or BSPP.
2. Check the threads for taper. Threads that visibly narrow = NPT. Straight, parallel threads = BSPP (or ORFS, distinguished by the flat sealing face).
3. Measure across the threads and count threads per inch. Comparing this against a thread chart is the most reliable way to confirm size and standard when the visual cues alone aren’t conclusive.
4. When in doubt, bring the old fitting in. Matching a physical sample against reference gauges is faster and more reliable than guessing from a description over the phone.

Getting the thread standard right matters more than it might seem — a connection that looks “close enough” and gets forced together can damage both fittings, and a leak that shows up hours or days later after a system is pressurized and back in service is a far more expensive problem than a five-minute check up front.