This part of ISO 5692 specifies the requirements for the attachment of agricultural non-balanced trailers and implements by means of hitch rings having a 50 mm hole centre and 30 mm ring diameter to the rear of a towing vehicle equipped with either a hook in accordance with ISO 6489-1 or a piton-type coupling as specified in ISO 6489-4. Its purpose is to ensure the interchangeability of mechanical connections on agricultural towed vehicles. This part of ISO 5692 is applicable to rings whose coupling point is below the centre-line of the rear axle and below the power take-off (PTO) of the tractor. NOTE Other International Standards are under development for rings coupled above the PTO.