Lock nuts DIN 981-14H zinc plated blue M50x1,5

DIN 1804 slotted nuts are round, unhardened, unground machine elements with four slots (= grooves) for the axial securing of shaft-hub connections, e.g. of gears on a shaft. They have a large internal diameter but a small external diameter. The internal thread is a metric fine thread. Slotted nuts are fitted using a hook spanner.

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.