With ISO metric screw threads to BS 3643, 1 mm to 20 mm diameter. Dimensions, tolerances, mechanical requirements for countersunk, raised countersunk, pan and cheese head screws with slotted heads, and countersunk, raised countersunk and pan head screws with recessed heads. Dimensions, tolerances, general requirements for square and hexagon machine screw nuts (pressed type). Checking recess penetration, dimensioning of 90° countersunk heads, standard sizes. See BS 1981, BS 3692.

1.1 The provisions of this British Standard are applicable to machine screws and machine screw nuts having ISO metric threads. 1.2 Dimensions and tolerances are given for machine screws in the following ranges: Table 1 — Machine screws. Metric series Machine screw type Head style Diameter range Slotted head screws Countersunk head Raised countersunk head Cheese head M1 (1 mm) to M20 (20 mm) Pan head M2.5 (2.5 mm) to M10 (10 mm) Recessed head screws Countersunk head Raised countersunk head M2.5 (2.5 mm) to M12 (12 mm) Pan head M2.5 (2.5 mm) to M10 (10 mm) 1.3 Dimensions and tolerances are also given for square and hexagon machine screw nuts, pressed type, within the diameter range M1.6 (1.6 mm) to M10 (10 mm). NOTE Details of precision hexagon nuts are given in BS 3692, “ISO metric precision hexagon bolts, screws and nuts??. 1.4 Mechanical properties are specified for steel, brass and aluminium alloy machine screws and machine screw nuts. 1.5 Appendices are included relating to the method of checking recess penetration with standard gauge points for machine screws, the dimensioning of 90° countersunk heads, standard sizes and the BSI policy statement on screw threads and the metric system.