When the arched surface contacts the top of the common nut or bearing surface, wrenching flattens the arch, deflecting the nutDeflects threads from their true helix causing them to firmly grip the bolt threads.The nut takes a permanent set and must be wrenched for further movement. Spins freely with fingers until making contact with the bearing surface. 1/2 to a full turn with a wrench will lock it securely. Constructed of high quality steel, hot-dip galvanized.