An attractive aluminum crank with hollow arms for lightweight, rigidity, and durabilityThe newly designed crank arms offer an optimized balance between lightweight and efficiency. The crank, formed with hollow aluminum technology, is anodized with a beautiful gloss black anodized finish, giving it a luxurious look. The resin ribs on the back of the chainrings are SHIMANO 105's unique structural design that achieves both thorough weight reduction and crisp shifting performance.