according to DIN 267, part 4
Hexagon nuts with nominal thread diameter d ≥ 5 mm must be marked with the property class on the bearing surface or on the side. Embossed markings must not protrude beyond the bearing surface of the nut.
For hexagon nuts with nominal thread diameter d ≥ 5 mm acc. to DIN 934 and DIN 935 made from free-cutting steel, the marking must also include a groove on one chamfer of the nut (up to property class 6).
