All-mountain SLX Hollow Tech II chainset is tough & aggressive yet also lightweight & excellent value The Hollow Tech II Chainset features hollow forged crank arms which are both lightweight & rigid whilst being incredibly strong & durable Hollow Tech II integrated bottom bracket design uses a wide bearing placement with a large axle diameter for increased stiffness efficiency & added durability 10-speed DYNA-SYS chainrings HG-X chainring with patented spike pins give smooth & fast gear shifts under load We recommend that the bottom bracket is initially installed by a bike shop to ensure perfect facing & fit For use with 10-speed HG-X MTB chains only 50 mm triple ring chain line for use in conjunction with 135 / 142 mm O.L.D.