This replaces the big cogwheel on the filawinder and adds a hook that grips into the spool. Its made for Innofil spools but you can also cut a little hole in the side any spool. This really helps the continuous winding without slipping. Its based on the original Filawinder file The cylindrical section has also been shortened because its no longer necessary to squeeze the spool onto it. Also check that the arm doesn't rip of components from the board the spacing of the motor and cogs could be different.