Screw: hexagon socket head shoulder

ISO 7379

ISO 7379 - Hexagon socket head shoulder screws

Hexagon socket head shoulder screws of property class 12.9, with a ground shoulder toleranced f9. The screw is a locating pin and a fastener in one: the shoulder runs in a bore and takes the shear load, while the thread under it, one size smaller than the shoulder, only pulls the joint together; this is what carries the pivots of links and levers, the guides of stripper plates and the moving parts of jigs and moulds. A size is the pair ds x l, as the designation of the standard writes it. The shoulder diameter brings the whole screw with it - the thread it carries, from M5 under a 6,5 mm shoulder to M20 under a 25 mm one, the head diameter dk, the head height k, the socket size s, the key engagement depth t and the thread length b - and the shoulder length says how thick a part the screw may locate. The thread length does not follow the length, as it does on a cap screw: it is fixed per shoulder diameter, because the thread is only what holds the seated shoulder down. Covers shoulder diameters 6,5 to 25 mm with shoulder lengths from 10 to 120 mm, the two smallest shoulders ending at 40 and 50 mm. The head may be plain or knurled, which is the only reason the table gives two head diameters; the shoulder length is toleranced from nominal to nominal + 0,25 mm. Catalogue sizes with shoulders of 6, 12 and 24 mm, and the small 4 mm with M3 and 5 mm with M4, are additions of manufacturers and are not part of the standard. Because of its shape the screw cannot be tensile tested, but meets every other requirement of class 12.9. The first edition of 1983 is still the current one.