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 70 degree spider arm for optimal rigidity 11-speed DYNA-SYS11 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 11-speed HG-X MTB chains only With a 51.8 mm double ring chain line ideally suited for 27.5+ bikes with Boost 148 mm O.L.D.