Size overview: Crank length: 113 mm, 118 mm, 121 mm, 126 mm. Hollowtech crank and Octalink bottom bracket axle interface. Lightweight cranks reduce the overall weight of the bike, particularly the rotating mass that is crucial for acceleration. The challenge is to lower the weight of the crank without compromising stability and durability. Shimano's state-of-the-art forging technology provides an ideal solution with the Hollowtech crank. Just like a high-quality frame tube, the hollow arm crank is extremely stable and durable while being very lightweight. The bottom bracket also plays an important role in achieving maximum stiffness in the crank. In Hollowtech cranks, the connection to the bottom bracket is made not through the traditional square taper, but through a thicker eight-point spline that engages with the counterpart on the hollow axle of the bottom bracket. This system is called Octalink.