A hitch ball engaging assembly provides a socket to receive a hitch ball with at least one locking element. A rotatable locking collar rotates between first and second positions respectively to move the locking element between a locked state and an unlocked state. A latch can be provided to retain the collar in the first and/or second positions. The locking element(s) may be ball(s) in holes in the socket and the collar has cam surfaces to move the ball(s). The hitch ball engaging assembly may particularly be used in an adapter to interconnect a pin connector of a fifth wheel coupling to the hitch ball of a gooseneck coupling. Here, an extension member is provided with a pin connector assembly to secure the fifth wheel pin on one end and the hitch ball engaging assembly on the other end. The invention includes methods accomplished by these structures.