Bolt with split pin hole h11 ISO 2341B-steel zinc plated blue 20x40

The tolerance grade is indicated by numbers ranging from 1 to 18. As the number increases, the size of the tolerance zone increases. The size of the tolerance depends on the nominal dimension. The tolerance system for internal and external dimensions is standardised in accordance with DIN EN ISO 286. The tolerance zones for external dimensions are indicated by lower-case letters followed by numbers.

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.