A coupling that includes a housing with a cutout; a cylindric shaft extending transversely to the cutout through aligned openings; a hook having a width which is less than the width of the cutout and which has a receiving opening with a diameter corresponding to the shaft diameter that is received in the opening. An insertion opening is provided that has a width which is less than the shaft diameter and which is oriented at an angle relative to a direction of pull by loading the hook. A part of the shaft that is disposed in the cutout is provided with opposing flats with a mutual spacing which is less than the width of the insertion opening. The shaft is arranged for longitudinal manual displacement against the action of a spring, from a first position where the flats are located outside the cutout to a second position where the flats are in the cutout.