This bolt is identifiable by the ridge or surrounding the bolt head, this built-in washer under the head of the Bolt acts to distribute the clamping load over a greater area. A flange bolt is designed to provide the same holding power as a washer. Zinc plating, retards the corrosion rate in a normal atmosphere. Class 10.9 has a minimum tensile strength of 1040 MPa, or approximately equivalent to SAE Grade 8.