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 plus chainrings HG-X chainring with patented single spike pin 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