5/8"-18 18-8 Stainless Steel Fine Thread Type C Lock Nuts (4 pcs.)

Diameter: 5/8"
Diameter 2: 1-1/16"
Thickness: 9/16"
Material: Stainless Steel
Driver Type: 15/16" Wrench
Thread Size: 18 (Fine)
Hardness: 18-8
Style: Type C
Type: Lock Nut

Box of 4.

A lock nut is a nut that resists loosening under vibrations and torque.