Cylinder screws hexagon socket fine thread ISO 12474-12.9 tempered black M8x20 mm

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.

The number before the decimal point, multiplied by one hundred, gives the nominal tensile strength value in N/mm². The number before the decimal point, multiplied by the number after the decimal point and multiplied by 10, gives the nominal 0.2% yield strength value in N/mm². The number after the decimal point indicates the yield strength as a percentage of the tensile strength.