Grade 8 nylon-insert steel hex locknuts. 9/16"-18, zinc-yellow coating. The nylon insert in these hex nuts eliminates the worry of vibration loosening the nut. They also are reusable. These Grade 8 high-strength steel hex nuts also offer greater strength and durability than their Grade 5 counterparts. The zinc-yellow chromate coating offers a high level of corrosion resistance and rust protection.