ORFS Fittings
O-Ring Face Seal Explained
ORFS (O-Ring Face Seal) fittings explained: how they work, why they outperform flare fittings, dash sizes, and how to identify and specify them correctly.
How ORFS Fittings Work
ORFS fittings seal on a flat face with an O-ring. Here's how the seal works and how to specify the correct fitting.
Understand the Seal Mechanism
ORFS fittings use a flat face with a groove that holds an O-ring. When the fitting is tightened, the O-ring is compressed against the mating flat face — creating a metal-to-metal contact plus O-ring seal. The O-ring does the sealing, NOT the threads.
Identify the Dash Size
ORFS fittings are specified by dash size, same as hose: -4 (1/4″), -6 (3/8″), -8 (1/2″), -10 (5/8″), -12 (3/4″), -16 (1″), -20 (1-1/4″), -24 (1-1/2″), -32 (2″). The dash number refers to the tube/hose size, not the thread.
Check the Thread Type
ORFS fittings use a UNF/UN thread form (SAE J1453 standard). The thread is straight (parallel), not tapered. Common thread sizes: -4: 9/16-18 UNF | -6: 11/16-16 UNF | -8: 13/16-16 UNF | -10: 1-14 UNS | -12: 1-3/16-12 UN | -16: 1-7/16-12 UN | -20: 1-11/16-12 UN | -24: 2-12 UN.
Check the O-Ring Groove
Every ORFS fitting has a visible O-ring groove on the flat face. The O-ring sits in this groove. When you look at an ORFS fitting, you should see: flat face + O-ring groove + O-ring. If you don't see a groove, it's not ORFS.
Distinguish ORFS from SAE Flare (JIC)
ORFS and SAE 37° flare (JIC) are often confused. ORFS: flat face with O-ring. JIC flare: 37° cone seat, no O-ring. Both use the same dash sizing and similar thread forms — but they are NOT interchangeable. Look for the flat face and O-ring.
Check Torque and O-Ring Condition
ORFS fittings need correct torque for a proper seal. The O-ring must be in good condition — a worn or cut O-ring will leak. Always replace the O-ring when reconnecting an ORFS fitting. We stock replacement O-rings.
Technical Specifications
| -4 (1/4") | Thread: 9/16-18 UNF | O-ring: 0.364 ID x 0.070 CS | Torque: ~18-24 Nm |
| -6 (3/8") | Thread: 11/16-16 UNF | O-ring: 0.487 ID x 0.070 CS | Torque: ~34-40 Nm |
| -8 (1/2") | Thread: 13/16-16 UNF | O-ring: 0.609 ID x 0.070 CS | Torque: ~54-60 Nm |
| -10 (5/8") | Thread: 1-14 UNS | O-ring: 0.755 ID x 0.070 CS | Torque: ~75-85 Nm |
| -12 (3/4") | Thread: 1-3/16-12 UN | O-ring: 0.924 ID x 0.070 CS | Torque: ~110-125 Nm |
| -16 (1") | Thread: 1-7/16-12 UN | O-ring: 1.171 ID x 0.070 CS | Torque: ~150-170 Nm |
| -20 (1-1/4") | Thread: 1-11/16-12 UN | O-ring: 1.468 ID x 0.070 CS | Torque: ~200-230 Nm |
| -24 (1-1/2") | Thread: 2-12 UN | O-ring: 1.718 ID x 0.070 CS | Torque: ~270-300 Nm |
| Standard | SAE J1453 (O-Ring Face Seal) — thread and O-ring dimensions |
| O-Ring Material | Nitrile (NBR) standard; Viton (FKM) for high temperature; EPDM for phosphate ester fluids |
Why ORFS Fittings Are Better
ORFS fittings have become the standard for modern mobile hydraulics. Here's why: 1. Metal-to-metal contact: The flat faces contact metal-to-metal, which provides a positive stop and prevents over-tightening. 2. O-ring seal reliability: The O-ring absorbs vibration and movement better than metal-on-metal flare seats. Less prone to loosening under vibration. 3. High-pressure capability: ORFS fittings reliably handle pressures up to 6000 psi (420 bar) and beyond. 4. Reusable: Unlike flare fittings that can crack at the cone after repeated assembly, ORFS fittings can be disassembled and reassembled multiple times (just replace the O-ring). 5. Leak prevention: The O-ring seal is more forgiving of minor surface imperfections than metal-on-metal seals. If your equipment uses ORFS fittings, don't substitute flare fittings — the seal mechanism is different and a substitution will leak.
Common Mistakes to Avoid
1. Confusing ORFS with SAE 37° flare (JIC): Check for the O-ring groove. ORFS has one; flare doesn't. 2. Reusing a damaged O-ring: A cut, flattened, or hardened O-ring will not seal. Always replace. 3. Using the wrong O-ring material: Nitrile is standard, but high-temperature or chemical applications need Viton or EPDM. 4. Over-tightening: Metal-to-metal contact means the fitting stops when the faces meet. More torque doesn't improve the seal — it just distorts the fitting. 5. Using the wrong dash size: ORFS dash size refers to tube size, not thread. Double-check before ordering.
Related Products
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Need ORFS fittings or O-rings?
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