This standard BS 57:1951 Specification. B.A. screws bolts and nuts is classified in these ICS categories:
21.060.10 Bolts, screws, studs
21.060.20 Nuts
Section 1 of this British Standard specifies requirements and dimensions for both ferrous and non-ferrous screws, bolts and nuts.
Heads: cheese, round, countersunk, raised-countersunk, hexagonal; hexagonal nuts, ordinary and locknut; range No. 0 to No. 16 B.A. Standard lengths of screws.