A coupling device is often referred to as a hitch or hook. It may be installed only on vehicles for which the manufacturer agrees to have such equipment (see information on registration certificate). In normal passenger cars and vans only a 50 mm hitch is allowed, but larger cars may have two other types. Coupling devices should only be mounted on a car by professionals. After installation, the vehicle must be brought to inspection station to take out the equipment and update the registration certificate. The coupling device must not obscure the registration plate; however, a hitch (hook)which, if used separately, may be obscured by a registration plate, it has ti be removable.