How to Identify a Hydraulic Fitting: JIC, ORFS, ORB and NPT
Four fitting families look almost identical at a glance. How to measure thread OD and pitch, read the seat, and tell JIC, ORFS, ORB and NPT apart - plus the -6 JIC/-6 ORFS mixup that fools even published charts.
Four hydraulic fitting families — JIC, ORFS, ORB and NPT — can look almost identical at a glance: similar dash sizes, similar hex nuts, similar tube diameters. But they seal differently, thread differently, and are not interchangeable, even at what looks like the same size. Match the wrong family and you get a fitting that threads on part-way, binds, and either won’t seal or won’t come back apart cleanly. Here’s how to actually identify what you’re holding — by measurement, not by guessing from the dash number.
How to measure a fitting
Three checks, in order — OD, thread pitch, then the seat.
- Measure the tube OD (or the port’s nominal size) with calipers. This narrows down the dash size, but not the family — a -6 fitting exists in JIC, ORFS and ORB, all with roughly the same 3/8” tube. Note that the thread alone will not finish the job: JIC -6 and ORB -6 are both 9/16-18, and only ORFS -6 differs at 11/16-16. Two families sharing one thread is exactly why the seat, not the thread, is the deciding test in step 3.
- Count threads per inch (TPI) with a thread pitch gauge, and measure the major (outside) thread diameter. OD plus TPI gives you the exact thread callout — for example 9/16-18 — which you can check against the tables below or the full chart linked above to see which family it belongs to.
- Read the seat. This is the part a thread measurement alone can’t tell you — two families can share a thread series but seal completely differently. Look inside the fitting: a cone means JIC, a flat face with a captured O-ring means ORFS, a straight thread ending in an O-ring at the base means ORB, and a visibly tapering thread with no O-ring at all means NPT.
The four seat types
The seat is what actually seals the joint — and it’s the one thing a thread measurement can’t tell you.
JIC — 37° flare (SAE J514)
JIC seals metal-to-metal: a 37° cone on the male fitting presses directly into a matching 37° flare on the female tube end. There’s no O-ring anywhere in the joint — the seal is entirely the two matched cones under torque. It’s the most common hose-end fitting in hydraulics, and it shares its flare angle and thread series with AN (aerospace and performance-aftermarket) fittings.
A male cone seats directly in a matching female flare — no O-ring, the metal-to-metal contact is the seal.
ORFS — O-ring face seal (SAE J1453)
ORFS seals on a flat face: a captured O-ring sits in a groove on one face and is squeezed against the other fitting’s flat face when the nut is torqued. There’s no cone and no metal-to-metal seal — the O-ring does all the sealing work, which makes ORFS more tolerant of a nicked or scratched face than a flare fitting is of a damaged cone.
Two flat faces meet with a captured O-ring between them — no cone at all.
ORB — O-ring boss (SAE J1926)
ORB is a port connection, not a hose-to-hose joint: a straight (non-tapered) thread screws into a threaded port, and an O-ring seated at the base of the threads — where the fitting shoulders against the port face — does the sealing. Because the thread itself is straight and isn’t what seals the joint, ORB ports also accept adjustable fittings that use a locknut and backup washer instead of a fixed hex.
A straight-thread fitting screws into the port; an O-ring at the shoulder seals it, not the thread.
NPT — tapered pipe thread
NPT is the odd one out: the thread itself is tapered and does the sealing — there’s no O-ring at all. As the fitting is turned in, the taper wedges tighter against the port’s matching taper; thread sealant or PTFE tape is normally used to fill the microscopic gaps between thread flanks. A visibly conical thread with no O-ring groove anywhere is your tell.
Identification pitfalls
The mistakes that fool experienced people, not just beginners.
Same dash number, different thread
A -6 JIC and a -6 ORFS fitting are both nominally “3/8 inch,” and neither the dash number nor the tube size tells you which one you’re holding:
| Family | Dash | Tube OD | Thread |
|---|---|---|---|
| JIC | -6 | 3/8” | 9/16-18 |
| ORFS | -6 | 3/8” | 11/16-16 |
Same dash, same nominal tube size, different thread entirely — they will not interchange.
A circulating published chart gets this backwards
At least one widely-circulated fitting chart lists the JIC thread series under an ORFS heading — printing 9/16-18 for a “-6 ORFS” fitting, when the real ORFS -6 thread, confirmed independently by multiple fitting manufacturers, is 11/16-16. If a chart’s ORFS thread column matches its JIC column exactly, dash for dash, that’s the tell that it’s wrong — treat it with suspicion and confirm against the fitting in your hand.
AN and JIC are the same thread
AN (aerospace/military and performance-aftermarket) fittings share the identical 37° flare and thread series as JIC — you cannot distinguish an AN fitting from a JIC fitting by measuring the thread. Hose-end hex sizes are also not standardized for AN: unlike the tube-nut hex, which is consistent, a given AN hose end’s wrench size can differ from the tube-nut chart.
Quick identification table
A one-glance summary of what to look for.
| Family | Thread | Seal | Distinguishing feature |
|---|---|---|---|
| JIC (SAE J514) | Straight, UN/UNF | Metal-to-metal | 37° cone, no O-ring |
| ORFS (SAE J1453) | Straight, UN/UNF | O-ring | Flat face with a captured O-ring groove |
| ORB (SAE J1926) | Straight, UNF/UN | O-ring | O-ring at the base of a straight thread; port connection |
| NPT | Tapered | Thread itself, plus sealant | Visibly conical thread, no O-ring |
Tools for the job
Two measurements, two tools — the seat inspection just needs your eyes.
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Digital caliper
Measures tube OD and thread major diameter directly in inches or millimetres — the first number you need before the thread callout means anything.
Thread pitch gauge set
Lay a leaf against the thread and read the match — far more reliable than counting crests with a ruler, especially on a fine pitch.
Frequently asked questions
How can I tell a JIC fitting from an ORFS fitting?
Look at the seat, not the thread alone. JIC seals on a 37° cone with no O-ring; ORFS seals on a flat face with a captured O-ring. If you only have the thread to go on, measure it exactly — a -6 JIC is 9/16-18, while a -6 ORFS is 11/16-16, despite the matching dash number.
Can I thread a JIC fitting into an ORFS port, or vice versa?
No — don’t force it. Even where a thread starts to engage, the seat geometry is completely different, so the joint won’t seal correctly, and forcing it risks damaging both parts.
What tool do I need to identify a hydraulic thread?
A caliper for outside diameter and a thread pitch gauge for threads per inch. Together they identify the exact thread; the seat — cone, flat face, or taper — then tells you the family.
Is AN the same as JIC?
They share the same 37° flare and thread series, so you can’t tell them apart by thread measurement alone. AN is the aerospace/military and performance-aftermarket naming for the same flare geometry; tube-nut wrench sizes match, but hose-end hex sizes on AN fittings are not standardized the way JIC’s are.
Why does NPT need thread sealant when the others don’t?
NPT is the only one of the four that seals on the thread itself — the taper wedges tight as you turn it in, and sealant or PTFE tape fills the microscopic gaps between thread flanks. JIC, ORFS and ORB all seal on a cone, face or O-ring instead, so the thread’s only job is to pull the joint together.
Keep going
Bottom line: don’t trust the dash number or the tube OD alone — JIC, ORFS, ORB and NPT can share both and still use completely different threads and seats. Measure the thread OD and TPI, then confirm with the seat: a cone is JIC, a flat face with an O-ring is ORFS, a straight thread with an O-ring at the base is ORB, and a bare taper is NPT. Once you know the family, the wrench and torque chart has the rest.