5/8"-18 Zinc Plated Grade 8 Steel Fine Thread Nylon Insert Lock Nuts (5 pcs.)

Diameter: 5/8"
Diameter 2: 1-7/32"
Thickness: 49/64"
Material: Steel
Finish: Yellow Zinc
Driver Type: 15/16" Wrench
Thread Size: 18 (Fine)
Hardness: Grade 8
Style: Nylon Insert
Type: Lock Nut

Box of 5.

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