All-mountain SLX Hollow Tech II crank set 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 12-speed SM-CRM75 chainring (sold separately) SM-CRM75 chainring teeth feature ShimanoÔÇÃ-s 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 12-speed HG+ MTB chains only Super boost 56.5 mm single ring chain line for use in conjunction with 157 mm O.L.D.