Surface protection:

In accordance with DBL 9440.40 (silver-coloured Cr(VI)-free) → VDA 235-104.42
Corrosion resistance:

≤ M8 → approx. 480 hrs. with no base metal corrosion in accordance with DIN EN ISO 9227-NSS.
≥ M10 → approx. 720 hrs. with no base metal corrosion in accordance with DIN EN ISO 9227-NSS.
The specified corrosion resistances apply for the corrosion tests according to DIN EN ISO 9227-NSS (salt spray mist testing), at the earliest 24 h after coating in the "as coated" state, i.e. before sorting, packaging, transporting and/or assembly. These values can be reduced through inevitable handling and assembly processes. A transfer of the corrosion resistances from the salt spray mist test to real assembly and operating conditions is not possible in the majority of cases. When designing a connection both the combined materials and if necessary coatings as well as the environmental conditions during operation must be considered by the designer in the selection of a suitable corrosion protection coating.

Friction coefficient:

µges = 0.09-0.14 (VDA 235-101)

Flange head screws reduce the risk of pretensioning force loss when placed on the contact surfaces. The surface pressure generated under the screw head during tightening is low compared to conventional hexagon heads (without flange), as the force is distributed over a larger contact surface.

Advantage:

Setting reduced due to fewer parts to be connected compared to connections using washers.
The concave washer pressing against the contact surface increases the elasticity of the connection so that the setting/creeping movements that occur are counteracted and pretension loss is generally prevented.