Hex Head screws partial threaded DIN 931 / ISO 4014-8.8 thick layer passivated M20x230 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.

Conversion coatings (passivation) serve to protect the metal coating against white corrosion. A thick-film passivation in accordance with ISO 4042 offers nine times greater protection against white corrosion than a blue passivation. Additional sealants and/or topcoats, in turn, protect the conversion coating.

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).

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