Abstract: A locking coupling comprises a body (1) adapted for connection to a separate body, a coupling collar (2) rotatably mounted on said body (1) and adapted to cooperate with said separate body to hold it in axial connection with said body (1), a locking collar (4) mounted on said body (1) and longitudinally movable thereon between locking and unlocking position, bias means (8) that urges the locking collar (4) towards the locking position, and locking formations (11, 10) on the locking collar (4) and coupling collar (2) that interengage axially when the locking collar (4) is moved to the locking position so as to restrain the coupling collar (2) against rotation on said body (1). The locking collar (4) can be retained in the unlocking position by retention formations (5, 9) on the locking collar (4) and body (1) that interengage longitudinally. The locking collar (4) is held captive longitudinally on the body by The coupling collar, and the latter is held captive on the body by an internal circlip (3).