Tube Fitting Boss Seal

A standard application for an O-ring is sealing a tube fitting. There are industry standards for boss fittings, with a series of O-rings corresponding to each boss size.  AS4395 is a fitting end that corresponds with AS5202 bosses. O-ring sizes are detailed in SAE J1926. O-rings used as boss seals can withstand much higher application pressures because the threaded hardware mates to eliminate a clearance gap.