5/8"-18 Zinc Grade 2 Nylon Thin Lock Nuts LKNUT-128 (5 pcs.)

Diameter: 5/8"
Diameter 2: 1-1/16"
Thickness: 13/32"
Material: Steel
Finish: Zinc
Driver Type: 15/16" Wrench
Thread Size: 18 (Fine)
Hardness: Grade 2
Style: Thin Pattern Nylon Insert
Type: Lock Nut

Box of 5.

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