HV square washers DIN 6917-C45 steel tZn M12

For nuts, only a single digit is used, which indicates the maximum strength class of the bolt with which the nut can be used (a strength class 10 nut can be used with an 8.8 or 10.9 bolt, but not with a 12.9 bolt).

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.

In hot-dip galvanising, a zinc coating is applied to the component by immersing it in molten zinc and then spinning it off. DIN EN ISO 10684 restricts its application to steel fasteners with standard threads ranging from M8 to M64, as well as strength classes up to 10.9 for bolts and 12 for nuts. The average coating thickness for fasteners is 50 micrometres, which ensures corrosion protection for many years.