A coupling assembly includes a female member having a receiving end with an axially extending passageway and inwardly facing groove extending outwardly from said passageway in a position spaced from the receiving end. A split metal locking ring is positioned in the groove. A male member is sized to be received in said receiving end and includes a rib having a ramp where the ramp in a first embodiment curves outwardly to an apex and in a first alternate embodiment curves outwardly to a flat and in a second alternate embodiment increases in height in a linear fashion until a relatively short distance from the flat where it curves outwardly to meet the flat, the rib also has a shoulder tapering away from the forward end and inwardly toward the axis. Upon insertion of the male member into the female member, the split metal ring is expanded as it rides over the ramp, engages the cylindrical surface and retracts to a smaller diameter approaching its original size to engage the shoulder thereby locking the male member into engagement with the female member. A release sleeve is mounted on the male member and is axially movable relative thereto to push the split locking ring up and off of the tapering shoulder to thereby disengage the male member from the female member.