Hydraulic Fitting and Thread Identification: JIC vs. ORFS vs. NPT vs. BSPP

Grab the wrong fitting and you get a weeping joint, a blown seal, or crossed threads that ruin an expensive port. The hard part is that a JIC, an ORFS, and an SAE straight thread can all look nearly identical across a parts bin. This guide shows you how to identify a hydraulic fitting and its thread by the three things that actually matter: thread form, seat geometry, and how it seals.

Start With How It Seals, Not How It Looks

Every hydraulic connection seals in one of two ways, and knowing which one tells you half of what you need. A metal-to-metal seat seal relies on a machined cone or ball mating against a matching angle. An elastomer seal relies on an O-ring squeezed either in a face groove or against a chamfer. Tapered pipe threads are the odd family out: they seal on the threads themselves as they wedge together.

Once you know the sealing method, the thread count and seat angle narrow it to a single fitting type. That is the whole diagnostic tree.

The Four Families You Will See Most

JIC 37° (SAE J514)

The workhorse of North American hydraulics. A 37-degree flare seals metal-to-metal against a matching cone. Threads are UN/UNF straight (parallel), so the nut spins freely until the flares meet. If you see a straight thread and a distinct 37° cone, it is almost certainly JIC.

ORFS — O-Ring Face Seal (SAE J1453)

Built for high-pressure, vibration-heavy circuits where a flare would eventually leak. The male half has a flat face with an O-ring in a groove; the female nut has straight UN threads and a flat landing. No cone, no flare, just a flat face and a visible O-ring. That flat face is the dead giveaway.

NPT / NPTF — Tapered Pipe Thread

American tapered thread that seals on the thread flanks. The thread diameter visibly shrinks toward the end, and the count is coarse (e.g., 3/4″ NPT is 14 TPI). If a thread gauge rocks because the pitch diameter changes along the thread, you are looking at a taper. Thread sealant or PTFE tape is expected here; it is not a bandage.

BSPP (G) — British Straight Pipe Parallel

Common on imported and industrial equipment. Parallel threads with a 55° Whitworth form (rounded crests) instead of the 60° V of NPT. BSPP seals with a bonded washer or an O-ring against a 30° cone seat, never on the threads. Because the crest shape differs, a BSPP fitting threaded into an NPT port will feel wrong within two turns.

Quick-Reference Identification Table

The Three Measurements That Settle It

When the eye is not enough, three quick measurements resolve any fitting:

• Thread pitch — a thread pitch gauge tells 60° from 55° and coarse from fine in seconds.
• Thread diameter — measure the male OD (or female ID) with calipers. Pair it with pitch and the size falls out of any dash-size chart.
• Taper vs. parallel — measure the thread diameter at the first and last engaged thread. Equal means parallel; shrinking means tapered.

Shop tip: A basic thread pitch gauge and a set of digital calipers pay for themselves the first time they stop you from cross-threading a $200 manifold port. Keep both in the same drawer as your fitting kit.

Why Dash Sizes Confuse People

Hydraulic sizes are quoted in dash sizes — sixteenths of an inch of nominal tube OD. A “-8” fitting is 8/16″ = 1/2″ tube. But the thread that carries a -8 is not 1/2″: a -8 JIC uses a 3/4″-16 thread. Confusing the tube dash size with the thread size is the single most common ordering error, so always identify the thread independently of the dash number.

Mismatches That Look Right Until They Leak

Several thread pairs are close enough to start by hand but will never seal, and they cause most field failures:

• NPT into BSPP (or the reverse). Both are 1/2″ nominal, but 60° vs. 55° forms and taper vs. parallel mean they cross-thread and either weep forever or split the port.
• JIC 37° against SAE 45° flare. Automotive 45° flare fittings share thread sizes with some JIC parts but seal on a different cone angle. The joint feels tight and leaks under pressure because the cones never fully mate.
• BSPP against BSPT. Parallel vs. tapered British threads look identical at a glance; only measuring the diameter along the thread separates them.

When two halves thread together smoothly but the seat “bottoms” oddly or the fitting stands proud, stop and measure — a forced mismatch is how ports get scrapped.

Torque to the Seat, Not to a Number Alone

Identification also drives assembly. Metal-seat fittings (JIC) are set by the flats-from-finger-tight (FFFT) method — snug, then a defined fraction of a turn — because over-torquing flattens the flare and starts a leak. O-ring fittings (ORFS, SAE ORB) are torqued to compress the O-ring to its designed squeeze, not to crush metal. Tapered threads (NPT) are set by turns past hand-tight with sealant, never by brute force. Knowing the family tells you which rule applies.

Put a Name on It in Seconds

Once you have thread form, seat angle, and seal method, our Thread Identifier tool matches your measurements to the exact standard, and the SAE hose identification guide handles the hose on the other end. For sizing the assembly by flow, see our hydraulic hose sizing and pressure-drop guide. All three live under Fluid & Force.