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 ISO standard that replaced DIN 7991. 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.
