Arm Material: aluminum Arm Length: 160mm, 165mm, 170mm, 172.5mm, 175mm Chainring Sizes: 50 / 34t Rings: 2 BB Type: 68mm threaded Built for Shimano 105 drivetrains, the Shimano 105 FC-R7100 12-Speed Crankset provides powerful, smooth shifting as we push the pedals to the max. Its 50/34T chainrings are built with a unique design for minimal weight and max power while achieving a perfect balance of stiffness, durability, and rotational performance. Since looks matter, too, Shimano gave this aluminum crankset a black gloss anodized finish.