ORFS Fittings: Face-Seal Operation, Identification, and Use Cases
May 2nd 2023
ORFS fittings are used when a hydraulic connection needs a controlled O-ring face seal rather than a thread seal or metal flare seal. ORFS stands for O-Ring Face Seal, and the sealing point is the flat face where the O-ring is compressed.
The threads on an ORFS connection provide clamping force. They do not create the fluid seal. That difference is the reason ORFS is often selected for high-pressure and vibration-prone hydraulic service.
How ORFS Sealing Works
The male ORFS fitting carries an O-ring in a groove on the flat face. The female ORFS side provides a matching flat face, often with a swivel nut. As the joint tightens, the O-ring is compressed evenly between the two faces.
Because the seal is at the face, thread sealant is not normally used on the threads. A leak usually points to the O-ring, the face surface, contamination, misalignment, wrong size, or damage from assembly.
Size and Chart Checks
ORFS sizes are commonly referenced by dash size, tube outside diameter, and straight UN or UNF thread size. The dash size is useful, but it should not be treated as the only identification point.
When checking an ORFS fitting, confirm the dash size, thread diameter, thread pitch, tube size, and pressure class. Larger sizes may have different pressure limits, so the chart has to be read as a complete specification rather than a simple thread list.
How to Identify ORFS Fittings
The easiest visual clue is the flat sealing face. A male ORFS end has a visible O-ring or an O-ring groove on the face. A female ORFS end has a flat internal face and often a swivel nut.
ORFS is often confused with JIC because both may appear on hydraulic hose assemblies. JIC uses a 37 degree cone seat, while ORFS uses a flat face and O-ring. ORB is another common confusion point because it also uses an O-ring, but ORB seals at a port, not between two flat fitting faces.
ORFS Compared With Other Connections
Compared with JIC, ORFS usually provides stronger leak resistance in vibration and pressure cycling because the elastomer seal can maintain contact across small movement. Compared with NPT, ORFS avoids thread-based sealing and does not depend on sealant filling a spiral leak path.
ORB is useful at a boss port, while ORFS is useful between fitting ends or hose assembly connections. The right choice depends on where the seal needs to happen: port, flare seat, face seal, or tapered thread.
Installation and Leak Prevention
Before assembly, inspect the O-ring, face, threads, and alignment. Replace cut, flattened, swollen, or hardened O-rings. Keep the face clean because a scratch or metal chip can create a leak even when the fitting is the right size.
Steel and stainless versions are selected based on corrosion exposure, pressure, and fluid compatibility. O-ring material also matters. Buna-N, FKM, and other elastomers handle different fluids and temperatures, so the O-ring should be specified for the actual service.
Where ORFS Works Best
ORFS is a good choice for mobile hydraulics, industrial systems, and high-pressure environments where leak control is more important than choosing the lowest-cost fitting style. It is less attractive when the system is low pressure, the connection is rarely disturbed, or O-ring material compatibility cannot be confirmed.
It can be reused only after inspection. The threads may be serviceable, but the O-ring and sealing face decide whether the connection should go back into service. Do not replace JIC, ORB, or NPT with ORFS unless the mating parts and seal locations are designed for that conversion.