Covers screws in diameters from numbers 2 to 18 and lengths up to 120 mm. The head varieties are countersunk, raised countersunk and round. Materials and mechanical properties are included for steel, brass, aluminium alloy, silicon bronze and 18/8 stainless steel. Preferred diameter/length combinations, and details of recess penetration gauging for 'Pozidriv ' cross recesses are given in appendices.