A coupling assembly includes a first coupling member having a first exterior surface and a second exterior surface spaced from the first exterior surface by a rib having a first locking surface. A second coupling member includes an inwardly facing surface sized to receive the first coupling member and an inwardly facing annular groove having a second locking surface. The groove is configured to reduce stress risers in the second coupling member. A resiliently expandable locking ring is received in the inwardly facing annular groove and is engaged and expanded to a larger radial size by the rib upon movement of the first coupling member further into the second coupling member. The resiliently expandable locking ring is configured to retract in diametrical size to become trapped between the first locking surface and the second locking surface upon further movement of the first coupling member into the second coupling member.