Flange Nuts have internal threads that correspond to the external threads of a bolt. The type of steel and the treatment of the material during manufacture determine the strength & ability to perform. Most commonly, flange nuts are case hardened with a zinc or hot dipped galvanized finish. The flanged nut has an enlarged circular base for an increased bearing surface. The wide flange acts as an integrated, non-spinning washer. There are several styles of flange nuts. Serrated hex flange nuts act as a locking nut. The serrations are angled so that the keep the nut from rotating in a direction that would loosen the nut. These serrations increase the holding power of the nut by avoiding vibration. Another style of flange nut is a flange top lock nut. They are a style of prevailing torque lock nut that uses a non-circular shape as the locking mechanism. This non-circular shape makes it nearly impossible to thread these nuts onto a bolt without a wrench. The common grades for flange top lock nuts are A, B and C, denoted by dots on the corners or notches in the sides. The flange style top lock nut eliminates the need for a washer and is commonly used with grade 8 frame bolts.
Most fastener items are available loose by the pound at your local Joseph Fazzio's store.