Advanced Hollowtech II Design ( Hollow Duraluminum crank arm forging results in increased rigidity with reduced weight ). Aluminium anodized Chainrings. SG-X Chain Rings (Designed to maintain front SIS shifting performance with the super-narrow 10-speed chain). Bolt Circle Diameter: 110mm. Octalink crank arm mount. Forged aluminum/anodized Crank arms.