Slotted set screws with conical head DIN 551 / ISO 4766-stainless A4 M8x25 mm

Slotted screw drives are the oldest form of rotary drives for fastening screws. The Schltz is usually manufactured in a pressed or milled version. Because of its uneconomical processing method (slow, unwieldy), the slot is increasingly disappearing in favor of other drives (hexagon socket, cross slot, hexagon socket).

Only one number is used for nuts. This indicates up to which strength class of the screw the nut can be used. For example, you can use a nut strength class 12 with a screw 12.9, but not with a screw 14.9. If you use nuts with a strength class that is too low, there is a risk of the thread stripping. Higher ones can be used without hesitation, but should only be used if the load on the screw is above the yield point.

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.

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.