10-speed Super Narrow HyperGlide compatible cassette (remaining ranges also compatible with newer Ultegra-6700 drivetrain). Fits 9-speed spacing (older 9sp freehubs require spline shim). Single, 6-arm aluminum carrier (3 largest cogs) reduces weight and increases stiffness. Nickel plated steel cogs for increased durability. 235g @ 12-23t.