The HollowTech II Chainset features hollow forged crank arms which are both lightweight and rigid whilst being incredibly strong and durable. HollowTech II integrated bottom bracket design uses a wide bearing placement with a large axle diameter for increased stiffness, efficiency and added durability. HG-X chainring with patented spike pins give smooth and fast gear shifts under load. With a 48.8mm double ring chain line for use in conjunction with 135 / 142 mm O.L.D. We recommend that the bottom bracket is initially installed by a bike shop to ensure perfect facing and fit.