This British Standard specifies dimensions for a 7/2 - 9/2 in diameter king pin for fifth wheel attachment to semi-trailers for extra heavy duty.
NOTE 1. A fifth wheel king pin for attachment to semi-trailers for normal and heavy duty is covered in BS AU 1, 'Dimensions of 2 - 23/8 in diameter fifth wheel king pin for use with semi-trailers'. The clearance dimensions and fifth wheel positions are given in BS AU 3, 'Clearance dimensions and fifth wheel positions for tractors and semi-trailers'.
NOTE 2. The values specified in imperial units are to be regarded as the standard.