5/16" x 19/32" Black Oxide Grade 2 Steel Lock Washers (20 pcs.)

Diameter: 5/16"
Diameter 2: 19/32"
Thickness: 3/32"
Material: Steel
Finish: Black Oxide
Hardness: Grade 2
Type: Lock Washer

Box of 20.

The purpose for a lock washer is to prevent threaded fasteners from loosening by creating friction between the fastener and the mounting surface.