Countersunk screws hexalobe ISO 14581-04.8 zinc plated blue M4x20 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.

Blue galvanised finishes are produced either by electroplating in accordance with DIN EN ISO 4042 or by mechanical plating in accordance with DIN EN ISO 12683. For fasteners with a hardness exceeding 390 HV, there is a risk of hydrogen embrittlement during galvanising (electrolytic process). This necessitates specific measures (such as annealing), although these do not provide a 100 per cent guarantee against embrittlement.

TORX (from the English word ‘torque’) is the registered word mark for a screw drive profile, the standard designation for which is ‘internal six-lobe’ (English: ‘six lobe, internal socket’). With the six-lobe internal socket, the screw and tool are subjected to less radial stress than with the traditional internal hexagon, and consequently suffer less damage. Torque is transmitted more directly via the radial parts of the tooth flanks rather than via the faces of the hexagon.

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 lower yield strength in N/mm2. The number after the decimal point provides information about the yield strength, as a percentage of the tensile strength.