Fouriers CR-DX008-SK2-423 42 Tooth Cassette Conversion with 16 tooth Cog Red Turn your existing Shimano Cassette into a Mega range 40 or 42T A two piece design made for a stable and durable drivetrain - Chromo teeth mated to an Alloy carrier Comes with longer B-tension screw and redesigned 16T sprocket (CR-S005-16) for smoother shifting and tooth ratio For installation take out the 15T and 17T sprocket and install the 16T between the 13T and 19T, Add the 40/42T after the largest sprocket 110g