A high performance double chainset from the classic ATB group using the most advanced 10-speed Dyna-Sys chainrings Forged Hollow Tech II aluminium cranks offer unrivalled strength-to-weight ratio Lightweight construction with external super smooth bottom bracket bearings for efficient use Aluminium double anodized outer chainring with plated inner ring for excellent rigidity & durability Optimised Q-factor for double chainset HG-X chainring with patented spike pins give smooth & fast gear shifts under load Stiffness & strength increased with advanced design due to wider spaced bearings & oversized axle 104 / 64 PCD four-arm chainrings For use with 10-speed HG-X MTB chains only We recommend that this bottom bracket is initially installed by a bike shop to ensure perfect bottom bracket facing & fit Comes complete with bottom bracket for 68 & 73 mm frames