The main benefits of the hollow carbon construction are simple: Stiffness & weight savings. Youll also feel zero crank flex. Fitted to the arms are a pair of Semi solid AL7075 100% CNC process chainrings secured by AL7075 Torx T-30 alloy chainring bolts. The SL-K uses a BB30 & has a Q-factor at 145mm & a chainline of 44mm means smooth shifting with 9 or 10 speed Sram, Shimano drivetrains.