Ultegra SL Hollow Tech II chainset offers a fine balance of light weight & rigidity with incredible shifting performance Hollow Tech II allows the bottom bracket bearings to be spaced wider apart (outboard the frame) enabling the use of larger bearings & an increased axle diameter Their is also the benefit of easier installation &44; adjustment & maintenance Lightweight & rigid steel bottom bracket axle SG-X aluminium anodized chainrings available in 53-39T / 52-39T (FC6600 double)&44; 52-39-30T (FC6603 triple) & 50-34T (FC6650 compact) Available in 165 mm&44; 170 mm&44; 172.5 mm & 175 mm Aluminium chainring bolts Weight 797g (53 / 39T&44; 170 mm including bottom bracket)