5/16"-24 Black Chrome Plated Steel Fine Thread Nylon Insert Lock Nuts (6 pcs.)

Diameter: 5/16"
Diameter 2: 9/16"
Thickness: 11/32"
Material: Steel
Finish: Black Chrome
Driver Type: 1/2" Wrench
Thread Size: 24 (Fine)
Style: Nylon Insert
Type: Lock Nut

Box of 6.

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