#6 x 9/64" x 5/16" x 9/32" 18-8 Stainless External Tooth Lock Washers LWSS-066 (40 pcs.)

Diameter: 9/64"
Diameter 2: 5/16"
Thickness: 1/32"
Material: Stainless Steel
Hardness: 18-8
Nominal Size: #6
Style: External Tooth
Type: Lock Washer
Application: Round|pan|or binding head
Diameter 3: 7/32"

Box of 40.

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