Dyna-Sys specific (HG-X) 10-speed mountain drivetrain compatibility Hollow-forged, 2-tone aluminum arms with a reinforced spider and an integrated, HollowTech-II (HT2) bottom-bracket spindle for improved power transfer 4-arm 64/104mm BCD with anodized aluminum outer / composite-reinforced steel middle / steel inner HG-X chainrings with pins/ramps for precise shifting Included wide-stance bottom bracket cupset with outboard bearings offers increased rigidity (fits both 68/73mm with included spacers) and designed for a 50.0mm chainline (BB92 and BB30 adapter bearings available separately)