Male O-Ring Boss (ORB) Swivel 90 Elbow 3/8 Inch Hose X 3/8 Inch TubeORB (O Ring Boss) fittings are used in hydraulic systems to create a secure, leak proof seal and are especially useful in high pressure applications. They are made up of a male and female part, each with specific threading and sealing surfaces. The male part has a groove for an O ring, while the female part has a machined surface with a chamfer. When the two parts are mated, the O ring compresses into the chamfer to create a tight seal.