This standard BS EN 2138:2000 Washers, flat, in steel, cadmium plated is classified in these ICS categories:
49.030.50 Washers and other locking elements
This standard specifies the characteristics of flat steel washers, cadmium plated, for maximum operating temperature 235°C, for aerospace applications. They are intended for use primarily underneath nuts, for use underneath bolt heads the compatibility shall be checked.
