Countersunk screws CR H ISO 7046-2-stainless A4 M8x55 mm

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 term plain indicates a completely untreated, merely oiled, smooth surface for all DIN and ISO screws such as wood screws, hexagon head screws, threaded rods, nuts and many types of washers.

Phillips (PH) screws, standardized in ISO 8764 (blades) and DIN 7962 (Phillips recess), are widely used. For screws with a Phillips cross slot, the flanks of the cross slots taper as the depth of the slot increases. With the PH system, threaded and self-tapping screws that are difficult to access can be tightened and loosened even from a slight acute angle to the screw axis.

Austenitic stainless steels derive their different strength grades from cold working to varying degrees. The number 80 following the grade designation indicates the tensile strength as one-tenth for bolts. A bolt in strength class 70 therefore has a tensile strength of 700 N/mm². For nuts, the number 70 indicates a stress under test load of 700 N/mm².

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 A4 is classified as acid-resistant due to its molybdenum content of 2 per cent to 3 per cent. A4 cannot be heat-treated and achieves its various strength classes through cold working to different degrees.