Abstract: A ball fastened to a base plate is received within the socket of a trailer hitch, with a box shaped, open ended housing slipped over the exposed end of the tongue, hitch, and plate. The plate has a pierced tang that extends through the closed end of the housing and into a tubular extension projecting from the housing. A purchase item cylindrical, keyed, tumbler operated, lock slips into the bore of the extension and projects a key operated, retractable, transversely movable, shot bolt through the pierced hole of the tang. The lock is protected within the extension, and the apparatus has no parts exposed for tampering.