SAE ORB O-Ring Boss Fittings: Specs, Thread Chart & ID Guide
SAE ORB (O-Ring Boss) uses Straight UN/UNF (60-degree) threads with a o-ring compressed against machined boss face seal per SAE J1926 / ISO 11926. Thread dimension table and identification tips below.
Thread Sizes
| Dash Size | Tube OD | Thread |
|---|---|---|
| -2 | 1/8" | 5/16-24 UNF |
| -3 | 3/16" | 3/8-24 UNF |
| -4 | 1/4" | 7/16-20 UNF |
| -5 | 5/16" | 1/2-20 UNF |
| -6 | 3/8" | 9/16-18 UNF |
| -8 | 1/2" | 3/4-16 UNF |
| -10 | 5/8" | 7/8-14 UNF |
| -12 | 3/4" | 1-1/16-12 UN |
| -16 | 1" | 1-5/16-12 UN |
| -20 | 1-1/4" | 1-5/8-12 UN |
| -24 | 1-1/2" | 1-7/8-12 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
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.
Where SAE-ORB Falls Short
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 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).
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 Gets 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.
SAE ORB (O-Ring Boss): Common Questions
What is a SAE O-Ring Boss fitting?
A straight-thread fitting that seals with an O-ring compressed against a machined boss (flat surface) on the port. Defined by SAE J1926. Unlike NPT which seals on the thread taper, ORB threads only hold the fitting in place while the O-ring does the sealing work. This makes ORB connections more reliable and repeatable than NPT.
Is SAE ORB the same as ORFS?
No. ORB (O-Ring Boss) seals between a fitting and a port body using an O-ring on the boss face. ORFS (O-Ring Face Seal) seals between two tube fittings using an O-ring on a flat mating face. ORB is a port connection standard. ORFS is a tube-to-tube connection standard. Many modern hydraulic systems use ORB ports with ORFS tube connections. See the ORFS specifications for how the face seal connection works.
Reference data only. Verify thread dimensions with a thread identification gauge before making connections. Working with pressurized hydraulic systems involves serious injury risks including high-pressure injection, burns, and crushing hazards. This site does not replace manufacturer specifications, proper training, or employer safety procedures. See full terms of use.
Data sourced from SAE J1926, ISO 11926. Thread dimensions are nominal values. Always verify with a thread identification gauge before making connections.