This standard BS 325:1947 Specification for black cup and countersunk bolts and nuts is classified in these ICS categories:
21.060.10 Bolts, screws, studs
21.060.20 Nuts
Nominal sizes ¼ in to 1 in. Dimensions for cup head bolts with square, oval and nibbed shanks, and countersunk headed bolts with square and nibbed shanks for use on steel work and wood work; square and hexagon nuts. Lengths of thread and their tolerances, form of end of bolt shank, quality of steel.