Lock Washer, Lock Washer Type Internal Tooth Lock, Finish Zinc Plated, Material Steel, For Screw Size 5/8 in, Inside Diameter 0.64 in, Outside Diameter 1.045 in, Maximum Thickness 0.042 in, Dimensional Standards ASME B18.21.1, Material Grade/Class Not Graded, Pack Size Small Pack, Rockwell Hardness C40 to C50, System of Measurement Inch, Package Quantity 10 Type A Internal Tooth Lock Washers lock into the screw head to help prevent loosening. An excellent choice for use with small-head screws and fasteners, and for applications where a clean appearance is desired. Meet ASME B18.21.1 standard.