Abstract: 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 (i) a ramp tapering in a direction away from the forward end and away from the axis at an angle in the range of 10.degree. to 25.degree., (ii) a cylindrical surface parallel to the axis extending rearwardly from the ramp a distance of at least 0.010 and preferably 0.030 inch and (iii) a shoulder tapering away from the forward end and inwardly toward the axis.