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 For 11-speed DYNA-SYS11 SM-CRM70 chainring &40;sold separately&41; SM-CRM70 chainring teeth feature Shimanos new Dynamic Chain Engagement technology offering enhanced chain retention driving rigidity & highly efficient 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 53.4 mm single ring chain line ideally suited for 27.5+ bikes with Boost 148 mm O.L.D.