Marking of screws and nuts (according to ISO 3506)

Screws and nuts made from stainless austenitic steels must be marked.

Caution Only those fasteners marked to standard will have the desired properties. Products not marked to standard will often only correspond to property classes A2-50 or A4-50.

Hexagon head screws, and hexagon or hexalobular socket head cap screws from nominal diameter M5 must be marked. The marking must show the steel group, the property class and the manufacturer’s mark. Locking screws must be marked on the shaft or screw end.

Bolts from nominal diameter M6 must be marked on the shank or the end of the thread with the steel group, the property class and the manufacturer’s mark.

Nuts from minimal diameter M5 must be marked with the steel group, the property class and the manufacturer’s mark.

When the marking is made with grooves and the property class is not indicated, property class 50 or 025 will apply.

It is possible that certain nuts would not fulfil the proof load requirements because of fine pitch thread or the geometry of the nut. These nuts may be marked with the steel grade, but shall not be marked with the property class.

Other types of bolts and screws can be marked in the same way, where it is possible to do so and on the head portion only. Additional marking is allowed, provided it does not cause confusion.

Fasteners that do not fulfil the tensile or torsional requirements because of the geometry may be marked with the steel grade, but shall not be marked with the property class.

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