This is a new TsuMura professional .325 pitch .050-.058 gauge replaceable sprocket nose assembly that fits TsuMura and TOTAL SUPER bars that are .050 or .058 gauge guide bars and are "SR" "SK" type guide bars. You can tell if your guide bar is a "SR" or "SK" type bar because these letters will be part of the part number stamped on the tail end of your guide bar.