Parker SAE standard fittings with UN/UNF threads and screw-in connectors with O-ring are designed for connection with UNF screw-in threads. They are also known as O-Ring Boss (O.R.B.) connections. Correctly assembled, they offer as good performance as the best leak-free connections with screw-in threads. The sealing and retaining functions are separate for this type of connection. The threads are only responsible for the holding function. Sealing is provided by an O-ring seal, which is held in a specially designed chamfer on the top of the threaded fitting. Under pressure, the O-ring seal secures the only possible leakage path. The high compression of the seal ensures that the connection is leak-free at both low and high pressures.