Squares of try-square type in three grades of accuracy: AA, A, B; cylindrical squares in grade AA; solid form block squares in grades AA, A; open form block squares in grades A, B. Nomenclature, designation, sizes, material, manufacture, design, accuracy, marking, protection, testing.Cross References:BS 1133:Section 6BS 1133:Section 19BS 1134 BS 1452BS 3643Replaces BS 939:1962.Incorporates the following:AMD 4239 published 29 April 1983