Abstract: A device is disclosed for stopping rotation of a shaft (4) for moving a flexible shutter (16) between a retracted (18) and an extended position (20). The device includes a stop means (22) and an abutment means (24) for abutting with the stop means. The abutment means is secured so as to have a first position (36) and a second position (38). The stop means and the abutment means are arranged so that when the shutter is in the extended position (20) the abutment means (24) and the stop means (22) form a rigid engagement having an end (26) attached to the shaft (4). The rigid engagement stops the shaft (4) from rotating and thus prevents the shutter from passing the extended position.