This International Standard specifies widths across flats for hexagon products, for example hexagon head bolts and screws, hexagon nuts and hexagon flanged bolts, screws and nuts, to be used in the respective product standards. It also specifies a logical ratio between under head (or nut) bearing area (which determines the magnitude of the compressive stress on the bolted members relative to the clamping force applied by the fastener) and the tensile stress area of the screw thread (which governs the clamping force which can be developed by tightening the fastener for any particular strength class of fastener). This calculation technique was applied to each of the hexagon series so that a proper grading of bearing area/stress area ratios would be available to engineering designers