Abstract: A locking device for locking two mold halves in the closed position for a blow molding process by use of a shaft with at least one lug on one coupling member and a mating key hole in a second coupling member such that the lug passes through the keyhole and is rotated within said second coupling to lock by engaging the lug with a flange of the keyhole. The rotation of the lug being effected by a guide rod and co-operating guide slots such that as the shaft of the coupling member moves in the locking direction the guide rod is guided by the slots to rotate the lug into the locking position.