9/16"-18, Hex Flange Nuts Serrated Case Hard Coarse Z/P, ea

The flange nut is serrated to provide a locking action. On a serrated flange nut, the serrations are angled such that they keep the nut from rotating in the direction that would loosen the nut. Because of the serrations they cannot be used with a washer or on surfaces that must not be scratched.
Product Cross References: 57NR