5/16"-24 Zinc Plated Grade 2 Steel Fine Thread Kep Lock Nuts (12 pcs.)

Diameter: 5/16"
Diameter 2: 9/16"
Thickness: 17/64"
Material: Steel
Finish: Zinc
Driver Type: 1/2" Wrench
Thread Size: 24 (Fine)
Hardness: Grade 2
Style: Kep
Type: Lock Nut
Washer Diameter: 19/32"

Box of 12.

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