This European Standard specifies the characteristics of railway wheels for use on European networks. !Four steel grades, ER6, ER7, ER8 and ER9 are defined in this standard; for European freight wagon interoperability purposes only grades ER6, ER7 and ER8 are applicable. NOTE 1 Grade ER6 is not normally fit for the duty of application to freight wagons; it is normally applied in low axleload situations."""" !Certain characteristics are defined according to a category 1 or a category 2. Category 1 is generally chosen when the train speed is higher than 200 km/h. Freight vehicles running at speeds lower than 200 km/h generally use wheels of Category 2."""" The