Hex Head screws partial threaded ISO 1414-25CrMo4 (1.7218) zinc plated blue M30x250 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.

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).

Material 1.7218 is a quenched and tempered chromium-molybdenum alloy steel. Screws and nuts made from this material can be used according to DIN 267-13 / DIN EN 10269 up to 500°C (upper limit of the temperature range with specified yield strength and tensile strength) or 550°C (upper limit of the temperature ranges with specified elongation and creep strength limits).

This chrome-molybdenum steel is a tempered steel according to EN 10083, construction number 72 - construction, mechanical engineering, container steel. The steel is low-alloyed, It contains 0.25 mass percent carbon and 1 mass percent chromium. Furthermore, according to a guideline analysis, it contains 0.25 mass percent silicon and molybdenum as well as 0.7 mass percent manganese.