Technical specifications and scope of application for EN ISO 7090 flat washers
The international standard EN ISO 7090 regulates the parameters of normal-series flat washers belonging to accuracy class A. A distinctive design feature of these products is the presence of a chamfer on the outer contour. The standard covers fasteners with a hardness of 200 HV and 300 HV for nominal thread diameters from 5 to 64 mm.
EV Group China engineers recommend using washers with a hardness of 200 HV when assembling units with the following parameters:
- Bolts and screws of accuracy classes A and B with a strength class up to 8.8 inclusive.
- Nuts of accuracy classes A and B with corresponding property classes up to 8.
- Fasteners made of austenitic and corrosion-resistant steels with an identical chemical composition.
- Hardened screws intended for thread forming by plastic deformation.
For high-strength connections using bolts and screws of accuracy classes A and B with a strength class up to 10.9, as well as nuts up to class 10 inclusive, washers with a hardness of 300 HV supplied by EV Group China should be used.
If it is necessary to use sizes outside the scope of this standard, it is recommended to refer to ISO 887 specifications. It is important to consider that when mounting on soft materials or working with oversized installation holes, a preliminary engineering calculation of the suitability of standard EN ISO 7090 washers must be performed to ensure the required distribution of contact stresses.