5/16"-18 Polished 18-8 Stainless Steel Coarse Thread Nylon Insert Lock Nuts

Diameter: 5/16"
Diameter 2: 9/16"
Thickness: 11/32"
Material: Stainless Steel
Finish: Polished
Driver Type: 1/2" Wrench
Thread Size: 18 (Coarse)
Hardness: 18-8
Style: Nylon Insert
Type: Lock Nut

Box of 6.

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