- 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 & stainless steel and typically use Buna-N or Viton, 90 Durometer O-rings. 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.