5/16" x 19/32" x 11/16" 18-8 Stainless Steel External Tooth Lock Washers

Diameter: 5/16"
Diameter 2: 19/32"
Thickness: 1/16"
Material: Stainless Steel
Hardness: 18-8
Style: External Tooth
Type: Lock Washer
Application: Round|pan|or binding head
Diameter 3: 15/32"

Box of 16.

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