SAE ORB O-Ring Boss Fittings: Specs, Thread Chart & ID Guide
SAE ORB (O-Ring Boss) Thread Sizes
| Dash Size | Tube OD | Thread |
|---|---|---|
| -2 | 5/16-24 UNF | |
| -3 | 3/8-24 UNF | |
| -4 | 7/16-20 UNF | |
| -5 | 1/2-20 UNF | |
| -6 | 9/16-18 UNF | |
| -8 | 3/4-16 UNF | |
| -10 | 7/8-14 UNF | |
| -12 | 1-1/16-12 UN | |
| -16 | 1-5/16-12 UN | |
| -20 | 1-5/8-12 UN |
SAE ORB (O-Ring Boss) fittings use straight (non-tapered) threads with an O-ring that seats against a machined boss face to create the seal. Unlike NPT where the threads create the seal, ORB threads only hold the fitting in place while the O-ring provides a leak-free connection. This separation of sealing and holding functions makes ORB fittings significantly more reliable than NPT for hydraulic applications. ORB is one of the most common hydraulic fitting standards in North American mobile and industrial equipment.
When to Use SAE ORB (O-Ring Boss)
Use SAE ORB whenever the equipment port is a machined boss with a flat face and straight threads.
Standard on most North American hydraulic pumps, motors, valves, and manifold blocks.
Required when the equipment manufacturer specifies SAE J1926 ports.
SAE ORB (O-Ring Boss) Limitations
Requires a machined boss (port) on the equipment, cannot be cut into raw material like NPT.
O-rings must be compatible with the hydraulic fluid in use.
O-ring must be replaced if damaged during assembly.
Not compatible with NPT ports despite similar thread sizes.
How to Identify SAE ORB (O-Ring Boss) Fittings
Look for straight (non-tapered) threads with an O-ring groove on the male fitting near the shoulder. The port has a flat machined face with a counterbore for the O-ring. Threads measure the same diameter at first and last thread (no taper).
SAE ORB (O-Ring Boss) Measurement Tips
Always install a new O-ring when reassembling. Lightly lubricate the O-ring with clean hydraulic fluid before threading in. Torque to specification. Do not use thread sealant on ORB threads as the O-ring provides the seal.
What SAE ORB (O-Ring Boss) Is Confused With
ORB threads are the same UN/UNF form as JIC, but the seal mechanism is completely different. JIC uses a 37-degree metal cone. ORB uses an O-ring. Do not attempt to use a JIC fitting in an ORB port. The threads may engage but the seal will fail.
Data sourced from SAE J1926, ISO 11926. Thread dimensions are nominal values. Always verify with a thread identification gauge before making connections.