Hex Head screws with flange DIN 6921-8.8 coated zinc flake M8x55 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.

Zinc flake coatings are non-electrolytically applied coatings in accordance with DIN EN ISO 10683. Additional top coats and lubricants may be applied. As this is a non-electrolytic process, no hydrogen is produced which could cause the components to become brittle. This requires correct pre-treatment. The corrosion protection is 10 times greater than that provided by electroplated coatings of the same thickness.

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.