Lock nuts DIN 1804-stainless A2 M40x1,5

DIN 1804 slotted nuts are round, unhardened, unground machine elements with four slots (= grooves) for the axial securing of shaft-hub connections, e.g. of gears on a shaft. They have a large internal diameter but a small external diameter. The internal thread is a metric fine thread. Slotted nuts are fitted using a hook spanner.

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 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.