ORB Fittings — SAE Straight Thread O-Ring Boss Guide
How to identify SAE Straight Thread O-Ring Boss (ORB) fittings: a straight UNF thread with an O-ring that seats into a chamfered port for a leak-tight seal in medium and high pressure hydraulic systems.
Other fitting tiles
SAE Straight Thread O-Ring Boss fittings incorporate a port connection as recommended by the National Fire Protection Association (N.F.P.A.) for leak prevention in medium and high pressure hydraulic systems. ORB connections are commonly manufactured in carbon, nickel plated carbon and stainless steel and typically use Buna-N or Viton, 90 Durometer O-rings.
How to identify ORB
- A straight UNF thread — the thread diameter stays constant, it does not taper.
- An O-ring carried on the male connection (commonly Buna-N or Viton at 90 Durometer).
- A female port with a straight thread plus a machined surface and a chamfer where the O-ring seats.
How ORB seals
The male connection is a straight UNF thread with an O-ring. The female port has a straight thread and a machined surface to provide a smooth, flat, accurately located surface (minimum spotface), along with a chamfer where the O-ring seats. The seal is created when the O-ring is compressed into the chamfer when mating the male and female connection, providing a leak-tight seal.
The boss seal does the work, not the threads
Unlike tapered pipe threads, an ORB fitting does not seal on the threads. The straight UNF thread is purely mechanical — the leak-tight seal comes entirely from the O-ring being compressed into the chamfer of the port (the boss). No thread sealant is required.
Materials
ORB connections are commonly manufactured in:
- Carbon steel
- Nickel plated carbon steel
- Stainless steel
The O-rings are typically Buna-N or Viton at 90 Durometer.
Common applications
Port connections on pumps, valves, manifolds and adapters in medium and high pressure hydraulic systems, where the N.F.P.A. recommends the straight thread O-ring boss port for reliable leak prevention.
