3/8"-24 Zinc Plated Grade 8 Steel Fine Thread Nylon Insert Lock Nuts

Diameter: 3/8"
Diameter 2: 21/32"
Thickness: 15/32"
Material: Steel
Finish: Yellow Zinc
Driver Type: 9/16" Wrench
Thread Size: 24 (Fine)
Hardness: Grade 8
Style: Nylon Insert
Type: Lock Nut

Box of 8.

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