SFS Linsen Bohrschrauben ~DIN EN ISO 15481 SR2 A2 4,2x13

Stainless steel refers to alloyed or unalloyed steels that contain at least 10.5% chromium and less than 1.2% carbon. Colloquially, stainless steel is also referred to as stainless steel (NiRo), although not all stainless steel is the same as "stainless".

The internal square enables a good frictional connection and the screwdriver slips out of the screw head less easily than is the case with screws with a slot. The system was therefore more suitable for industrial use. A common application in Europe is self-drilling sheet metal screws for installing ventilation ducts.

Stainless steels are defined in DIN EN 10088-1 as iron alloys containing at least 10.5 per cent chromium and no more than 1.2 per cent carbon. The multi-part DIN EN ISO 3506 series of standards applies to mechanical fasteners made from stainless steels. Grade A2 is classified as non-acid-resistant. Austenitic stainless steels cannot be heat-treated and achieve their different strength classes through cold working to varying degrees.