Short answer
ORFS is a connection family that seals at the face with an O-ring. The flat face, O-ring groove, mating face and the correct seal work together; a matching thread size alone is not sufficient for a proper assembly.
Technical explanation
ISO 8434-3 is the relevant standard for O-ring face seal connections. The material and size of the seal must be compatible with the fluid, temperature and connection design. O-ring damage, groove contamination or mating face defects are inspection topics that can lead to leakage. ORFS and O-ring boss do not have the same sealing location. Compatibility should not be sought by changing the seal thickness or overtightening without the manufacturer's instructions.
Topic-specific checkpoints
| Item | Description |
|---|---|
| Sealing location | Face area of the connection |
| Seal | Correct size and material |
| Surface | Integrity of the groove and mating face |
| Identification | Distinguishing ORFS from ORB |
How is it assessed in practice?
When ordering spare parts, do not write only 'O-ring fitting'; specify the ORFS family, size and seal material. When examining a seal you have removed as a sample, bear in mind that it may have swollen or deformed in service. Refer to the product drawing to select the new seal. Check cleanliness and seal placement before assembly; do not touch with your hands to look for leaks under pressure. The decision to reuse or replace the seal must be made according to the manufacturer's method.
Original editorial recommendation; not a clause of a standard.
Frequently asked questions
Is every hydraulic connection with an O-ring an ORFS?
No. O-rings can be used in different positions in different connection families; the port and face design must be defined separately.
Source coverage
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S019
4 Easy Steps to Identify Hydraulic Threads Parker Hannifin · accessed 2026-10-19 PDF page 1-2: thread identification
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S073
ISO 8434-3:2005 ISO · accessed 2026-10-19 Abstract; O-ring face seal connectors