Everbilt 5/16-18x1-1/2 in. Zinc Hex Head External Hex Drive Flange Bolt 1-Piece

These serrated flange bolts are hex head bolts with a flanged washer face that has serrations on the bearing surface side. Designed for applications where vibration is present, the teeth grip the surface so that more effort is needed to loosen the screw than tighten it. The built in washer, in some applications, eliminates the need for a lock washer or lock nut.