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JIC and ORB Hydraulic Fitting Sizes

Guide · Updated October 28, 2026

Hydraulic hose and tube fittings use dash numbers, where the number is the tube OD in sixteenths of an inch: -4 is 4/16 = 1/4 in tube, -8 is 1/2 in, -16 is 1 in. JIC 37° flare fittings (SAE J514) seal on a 37 degree flared cone; the threads only hold the joint together. SAE O-ring boss (ORB, SAE J1926) ports seal with an O-ring on a straight thread and, for the common sizes, use the same UN threads as JIC. The values below are the standard J514 sizes published in fitting maker catalogs.

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Step by step

Clean the fitting: Remove dirt and old sealant so the threads and seat are visible.
Look at the seal: 37° cone = JIC; O-ring on a straight thread = ORB; tapered thread with no seat = NPT; 45° cone = SAE flare.
Measure the thread OD: Caliper the male thread crests or the female thread inside diameter.
Measure the pitch: Use an inch thread pitch gage; JIC and ORB are UNF/UN, NPT is 27, 18, 14, 11-1/2 TPI.
Check the seat angle: Use a seat angle gage; 37° and 45° look alike.
Read the dash size: Match the thread to the chart.

JIC 37° flare thread chart (SAE J514)

-2 (1/8 tube): 5/16-24
-3 (3/16): 3/8-24
-4 (1/4): 7/16-20
-5 (5/16): 1/2-20
-6 (3/8): 9/16-18
-8 (1/2): 3/4-16
-10 (5/8): 7/8-14
-12 (3/4): 1-1/16-12
-14 (7/8): 1-3/16-12
-16 (1): 1-5/16-12
-20 (1-1/4): 1-5/8-12
-24 (1-1/2): 1-7/8-12
-32 (2): 2-1/2-12

Male thread OD measures close to the nominal thread size; female thread inside diameter measures roughly one pitch smaller, for example about 0.69 in on a -8 (3/4-16) female.

SAE O-ring boss (ORB)

ORB ports and fittings use straight UN threads with an O-ring seated in a chamfer at the top of the port. For -4 through -16 the threads are the same as JIC: -4 7/16-20, -6 9/16-18, -8 3/4-16, -10 7/8-14, -12 1-1/16-12, -16 1-5/16-12. That means a JIC male will thread into an ORB port, but it will not seal there; always check whether the port has the O-ring chamfer.

How JIC, SAE 45°, ORB and NPT differ

JIC: straight thread, 37° flare seat, metal-to-metal seal
SAE 45° flare: often the same thread, 45° seat, mostly low pressure fuel and refrigeration lines
ORB: straight thread, O-ring seal in the port, best leak resistance at high pressure
ORFS (SAE J1453): flat face with an O-ring in the face
NPT/NPTF: tapered thread, seals on the thread with sealant or dryseal fit

Worked example: identifying a -8 fitting

The male thread measures 0.748 in over the crests and the pitch gage fits 16 TPI. That is 3/4-16. A 37° cone at the nose makes it a -8 JIC, which is a 1/2 in tube size. If the same 3/4-16 thread has an O-ring at the base instead of a cone, it is a -8 ORB.

Worked example: telling NPT from JIC

A male thread measures about 0.84 in at the large end, tapers, and fits 14 TPI. That is 1/2 NPT (pipe OD 0.840 in), not a JIC size. A tapered thread with a 1/16 in per inch taper on diameter is always pipe thread; JIC and ORB threads are parallel.

Machining ORB ports

ORB ports need a spotface, the straight thread and a precise O-ring chamfer, so most shops use a combination port tool for each dash size. Use a thread plug gage on the straight thread and check the spotface for a smooth, flat seat; a scratch across the chamfer will leak.

Common problems

Mixing 37° JIC with 45° SAE flare, sealing JIC threads with tape (the seal is on the cone, not the thread), threading a JIC male into an ORB port, and calling the tube size the thread size. Use a seat angle gage and pitch gage before ordering.

FAQ

What does -8 mean on a hydraulic fitting?

8/16 in, or 1/2 in tube OD. A -8 JIC thread is 3/4-16.

What thread is a -6 JIC?

9/16-18 UNF.

Are JIC and ORB threads the same?

For -4 through -16 the threads match, but they seal differently and are not interchangeable.

How do I check a thread pitch gage reading?

Check the gage itself before trusting a measurement: gage blocks set mics, calipers and indicators; build any stack free at gageblockcalc.com.

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General shop information only — follow your drawing, tool maker's data and your quality system.