A hex cap screw is a cap screw with a hexagonal head, designed to be driven by a wrench (spanner). An ASME B18.2.1 compliant cap screw has somewhat tighter tolerances than a hex bolt for the head height and the shank length. The nature of the tolerance difference allows an ASME B18.2.1 hex cap screw to always fit where a hex bolt is installed but a hex bolt could be slightly too large to be used where a hex cap screw is designed in. Materials are available in a wide variety for hex screws including LOW CARBON STEEL 4.6,4.8,5.6,6.8, ALLOY STEEL GRADE 8.8 & 10.9 ,BRASS, Hex Full Thread Screws are available in metric thread sizes ranging from M5 to M10, and lengths of between 15 mm up to 75 mm as standard. Non-standard dimensions are also available on request.