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 the bars are either the "FV" or "FK" type guide bars. You can tell if your guide bar is a "FV" or "FK" type bar because these letters will be part of the part number stamped on the tail end of your guide bar.