5/16" x 0.688" OD Low Carbon Zinc Finish Steel SAE General Purpose Flat Washer / CROSS-SECTIONAL SHAPE STYLE: 1 RECTANGULAR HOLE DIAMETER: 0.813 INCHES NOMINAL PERIPHERAL SHAPE STYLE: 1 ROUND CENTER HOLE SHAPE STYLE: 1 ROUND THICKNESS: 0.160 INCHES NOMINAL OVERALL DIAMETER: 0.688 INCHES NOMINAL END ITEM IDENTIFICATION: MRAP 3930-01-486-2151 HARDNESS RATING: 38.0 ROCKWELL C MINIMUM AND 45.0 ROCKWELL C MAXIMUM PART NAME ASSIGNED BY CONTROLLING AGENCY: WASHER,FLAT HARD REGULAR METRIC ZN MATERIAL: STEEL OVERALL SURFACE TREATMENT: ZINC OVERALL