5/16"-18 Zinc Plated Grade 2 Steel Coarse Thread Lock Nuts LNS-278 (20 pcs.)

Diameter: 5/16"
Diameter 2: 9/16"
Thickness: 9/32"
Material: Steel
Finish: Zinc
Driver Type: 1/2" Wrench
Thread Size: 18 (Coarse)
Hardness: Grade 2
Style: Center
Type: Lock Nut

Box of 20.

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