Socket head cap screws with flange and serrations FK100 M12x25

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.

Compared with a Phillips-head screw of the same size, a hex socket screw can withstand around ten times the torque. Hex socket screws are well suited to bolted joints where the screw heads are difficult to access due to the design of the structure. Hex socket screws can be countersunk to save space if protruding screw heads are a problem.

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.