Hex Head screws with flange and bottom head ribs St tempered black M8x12 mm

The wrench sizes for hexagon bolts and nuts are specified in ISO 272: 1982-01. The nominal wrench size on the workpiece (e.g. bolt, nut) is the same as that on the tool. However, there is some play between the two to allow the tool to be fitted without difficulty. The relationship between the nominal diameter d of the thread and the wrench size s is standardised in EN ISO 4014 and EN ISO 4017 for hexagon bolts, and in EN ISO 4032 for hexagon nuts (dimensions in mm).

Steel screws with underhead ribs: These have a minimum tensile strength of 1000 N/mm² and are case-hardened (surface hardness of at least 550 HV) to ensure that the ribs or locking teeth can fulfil their function. This is a key difference from standard screws in accordance with DIN 6921. Stainless steel screws and nuts: The stainless steel nuts and screws are available in the following strength classes: (50), 70, 80 and 100.

Steel is an iron-carbon alloy with a maximum carbon content of 2% by mass. The steels achieve their intended physical and mechanical properties through various hardening, annealing and tempering processes. It is also possible to harden the edge zone by surface hardening, case hardening or nitriding. Well-known steel grades are structural steels, free-machining steels, case-hardening steels, nitriding steels, tempering steels, tool steels and stainless steels.

The tempering process of screws and nuts (heating - holding - quenching - tempering) results in a thin baked oxide layer, which is referred to as tempered black. This surface condition is not a surface coating and therefore offers no corrosion protection.