SAE O-ring boss, ORB (SAE J1926-1)
A straight thread with an O-ring on a plain shoulder BEHIND the thread, screwed into a port with a flat spotface.
60 degree flanksParallelO-ring boss (straight thread port)
Confusion pair
ORB vs ORFS
Both seal on an O-ring and neither seals on the thread, which is where the confusion starts. The threads are a size apart at every dash, so they will not assemble - but the two ends often appear on the same fitting.
O-ring face seal, ORFS (SAE J1453)
A straight thread with a completely flat nose and the O-ring in a groove in that FACE.
60 degree flanksParallelO-ring face seal (flat face)
The three answers
What actually happens if you put them together
What interchanges
- Nothing. At every dash size the ORFS thread is a full size larger than the ORB thread of the same dash: a -08 ORB is 3/4-16 and a -08 ORFS is 13/16-16.
What threads together and will still leak or fail
This is a safety statement, so it is only made where it is sourced. Each item below either cites a published statement that the two are not interchangeable, or rests on the figures on the size pages showing an identical thread with a different seat.
- Neither will thread into the other, so there is no leaking combination between them. The failure with these two is a different one: fitting an ORB stud with the O-ring missing, or into a port with no machined spotface. The O-ring is the seal and the thread only carries the load, so a missing ring or a rough port face weeps immediately, and torquing the stud down to chase it damages the spotface and scraps the port.
What will not fit at all
- Every combination. The threads differ at every size, so an ORFS male will not start in an ORB port and an ORB stud will not start in an ORFS swivel.
- An ORFS male mated to any female without a flat face - a JIC swivel, for instance - will thread on where diameters happen to allow and has nothing to compress its O-ring against.
The check that settles it
Look at the nose. ORFS is dead flat with a shallow circular groove machined into the face. ORB has no groove in the face at all - its O-ring sits on a plain shoulder between the thread and the hex, and on a used fitting the ring is usually gone and only the shoulder is left.
Size by size
Where the threads match, and where they do not
No size in this pair will start on the other, so nothing here assembles by accident. Built from the published dimensions at page-build time, not from a hand-kept list.
| Size | SAE O-ring boss, ORB | O-ring face seal, ORFS | Will they assemble? |
|---|---|---|---|
| -02 | 5/16-24 UNF · 7.94 mm | No such size | Only one family has this size |
| -03 | 3/8-24 UNF · 9.53 mm | No such size | Only one family has this size |
| -04 | 7/16-20 UNF · 11.11 mm | 9/16-18 UNF · 14.29 mm | No - 20 TPI against 18 TPI |
| -05 | 1/2-20 UNF · 12.7 mm | No such size | Only one family has this size |
| -06 | 9/16-18 UNF · 14.29 mm | 11/16-16 UNF · 17.46 mm | No - 18 TPI against 16 TPI |
| -08 | 3/4-16 UNF · 19.05 mm | 13/16-16 UNF · 20.64 mm | No - 1.59 mm apart on diameter |
| -10 | 7/8-14 UNF · 22.23 mm | 1-14 UNF · 25.4 mm | No - 3.17 mm apart on diameter |
| -12 | 1 1/16-12 UN · 26.99 mm | 1 3/16-12 UN · 30.16 mm | No - 3.17 mm apart on diameter |
| -14 | 1 3/16-12 UN · 30.16 mm | No such size | Only one family has this size |
| -16 | 1 5/16-12 UN · 33.34 mm | 1 7/16-12 UN · 36.51 mm | No - 3.17 mm apart on diameter |
| -20 | 1 5/8-12 UN · 41.27 mm | 1 11/16-12 UN · 42.86 mm | No - 1.59 mm apart on diameter |
| -24 | 1 7/8-12 UN · 47.62 mm | 2-12 UN · 50.8 mm | No - 3.18 mm apart on diameter |
| -32 | 2 1/2-12 UN · 63.5 mm | No such size | Only one family has this size |
Diameters shown are the basic major diameter of the male thread. On a tapered thread that figure is defined at the gauge plane, which is not where a caliper naturally sits - the size pages carry the span published charts actually measure.
Detail
Everything each family carries
| Property | SAE O-ring boss, ORB | O-ring face seal, ORFS |
|---|---|---|
| Flank angle | 60 degrees | 60 degrees |
| Parallel or tapered | Parallel | Parallel |
| Seat | O-ring boss (straight thread port) | O-ring face seal (flat face) |
| Where it seals | The O-ring squashed between the fitting shoulder and the machined spotface of the port. The thread only holds the load. | The O-ring squashed between the two flat faces. The thread only holds the load. |
| Defined by | SAE J1926-1, ISO 11926-1 | SAE J1453, ISO 8434-3 |
| Sized by | Sized by dash number. The thread is identical to the JIC thread of the same dash - only the sealing end differs. | Sized by dash number for the tube outside diameter, but the thread is larger than the JIC thread of the same dash. |
Answers
Common questions
Will a SAE O-ring boss, ORB screw into a O-ring face seal, ORFS?
Neither will thread into the other, so there is no leaking combination between them. The failure with these two is a different one: fitting an ORB stud with the O-ring missing, or into a port with no machined spotface. The O-ring is the seal and the thread only carries the load, so a missing ring or a rough port face weeps immediately, and torquing the stud down to chase it damages the spotface and scraps the port.
Are SAE O-ring boss and O-ring face seal interchangeable?
Nothing. At every dash size the ORFS thread is a full size larger than the ORB thread of the same dash: a -08 ORB is 3/4-16 and a -08 ORFS is 13/16-16.
How do I tell them apart?
Look at the nose. ORFS is dead flat with a shallow circular groove machined into the face. ORB has no groove in the face at all - its O-ring sits on a plain shoulder between the thread and the hex, and on a used fitting the ring is usually gone and only the shoulder is left.
More pairs
Other fittings people mix up
Where these figures come from
Every value on this page was checked against 4 independent published sources:
- Hydraulic coupling identification chart E2/50101 - Gates, Gates Europe, 2004 (manufacturer, read 2026-08-27)
- Fluid Ports and Connectors Identification Guide - McGill Hose & Coupling, SAE J512, J514, J1453, J1926-1, ISO 228, ISO 7, DIN 2353, JIS (distributor, read 2026-08-27)
- Master catalogue: conformance, working pressure and torque tables - Tompkins Industries, SAE J514, SAE J1453, SAE J1926-1, SAE J1926-3, ISO 11926-1 (manufacturer, read 2026-08-27)
- Boss, face and flange O-rings: AS568 900 series and zero series - Global O-Ring and Seal, AS568 (manufacturer, read 2026-08-27)
Sources disagree: ORFS -08 male thread diameter.
- 22.0 mm (gates-idchart)
- 20.6 mm (apex-threadid)
- 20.8 mm (mcgill-id)
22.0 mm cannot be a 13/16 in thread, whose basic major diameter is 20.64 mm, and the same chart gives a female inside diameter of 19.1 mm, which only fits the smaller figure. The outlier is treated as a misprint and excluded from the published span, and it is recorded here so nobody has to work that out twice.