BS 2L 87:1971 Specification for hexagonal bars for nuts, couplings and hollow machined parts of aluminium-copper-magnesium-silicon-manganese alloy (solution treated and precipitation treated) (free from peripheral and asymmetric coarse grain) (not less than 14 mm nor more than 36 mm across flats) (Cu 4.4, Mg 0.5,

standard by BSI Group, 08/31/1971