With a unique four arm spider and hollowtech ii construction putting strength just where its needed the fc 9000 chainset sets new standards for stiffness and low weight new 4 arm design for same stiffness with lighter weight hollowtech ii construction hollowglide chainrings 11 speed compatible same bolt circle diameter for compact and traditional double chainsets means that one crankarm fits all chainring sizes 50 34t 53 39t chainring sizes 1725mm crank arm length