Screw: hexagon socket countersunk head

ISO 10642

ISO 10642 - Hexagon socket countersunk head screws with reduced loadability

Hexagon socket countersunk head screws with reduced loadability, in steel and stainless steel, with metric coarse pitch thread, product grade A. The screw is driven by a hexagon key seated in a socket sunk into a 90 degree conical head, so the head pulls itself into a countersink and ends flush with the surface; this is what holds cover plates, lids, guards and every joint a hand or a moving part has to pass over. A size is the pair d x l: the thread diameter fixes the head diameter dk, the head height k, the socket size s and the key engagement depth t, while the length decides whether the screw keeps a plain shank or is threaded up to the head. The head is given two diameters: the theoretical one, where the cone would close on a sharp corner and to which the head height is measured, and the actual one the rim is turned to. Sinking the socket into so shallow a head is what limits the load the screw can take, which is what reduced loadability means here: the minimum ultimate tensile load of a size is 80 % of the load of a fully loadable screw of the same thread and property class. The reference thread length b is 2d + 12 mm up to M12 and 3d from M14 on, so that a partially threaded screw of the large threads can still be tensile tested. Covers threads M2 to M20 with nominal lengths 5 to 100 mm. Its German predecessor DIN 7991 was replaced by DIN EN ISO 10642 but draws a smaller head, a shorter thread and its own threads up to M24; the button head counterpart is ISO 7380-1.