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. Plain finish, or bare metal, may or may not have a coating of light oil to resist corrosion. Class 10.9 has a minimum tensile strength of 1040 MPa, or approximately equivalent to SAE Grade 8.