This is a new TsuMura professional .325 pitch .063-gauge replaceable sprocket nose assembly that fits TsuMura and TOTAL SUPER bars that are .063-gauge guide bars and fits the bars that are either the "SR" or "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.