General dimensions and tolerances of bolts, screws and nuts with ISO metric threads to BS 3643, in diameters of 1.6 mm to 68 mm (for the convenience of users requiring larger sizes, further information in relation to the derivation of tolerances is provided in an appendix). Mechanical properties are given in respect of carbon and alloy steel bolts, screws and nuts, but the dimensional requirements apply also to non-ferrous and stainless steel bolts, screws and nuts.