ISO 1103:2007 lays down the dimensions necessary for the compatibility of mechanical coupling devices between light trailers or caravans and towing vehicles, when the latter are fitted with a coupling ball. The clearance space around the coupling ball is intended to allow coupling and decoupling of towed vehicles, as well as safe operation during coupling and uncoupling of mechanical devices. ISO 1103:2007 applies to coupling balls designed to couple caravans and light trailers of categories O1 and O2 to vehicles of categories M or N. It does not necessarily apply to special trailers drawn by special vehicles.