This International Standard specifies dimensional requirements for the attachment of agricultural, non-balanced trailers and implements by means of hitch rings to the rear of towing vehicles equipped with a hook specified in ISO 6489-1. Its purpose is to ensure the interchangeability of the mechanical connections on agricultural towed vehicles. This International Standard is applicable to rings whose coupling point is below the centre-line of the rear axle and the power take-off (PTO) of the tractor. NOTE Other International Standards are to be developed for rings above the PTO coupling.