Flat discs with chamfer, normal row ISO 7090-steel 300 HV hot-dip galvanized 21

The combination of strength classes for flat washers with those for bolts and nuts is governed by ISO 898-3:2018, Table 1. Washers with a hardness of 300 HV are suitable for applications with heat-treated bolts and nuts (bolts up to 10.9, nuts up to Class 10). Applications involving bolts of strength class 12.9 and nuts of class 12 must be checked during installation.

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.