X1Tools Ultra-Hi-Performance Black-Oxide Grade 8 Steel Thin-Profile / Low Profile Nylon-Insert Locknuts / Stop-Nuts are made to resists loosening due to use or vibration without damaging threads thus prevent a fastener from backing off. (Also Known as lock nut, locking nut, self-locking nut, prevailing torque nut, stiff nut or elastic stop nut)