3/8"-16 Black Phosphate Grade 2 Nylon Insert Lock Nuts (286 pcs.)

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

Box of 286.

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