2-piece forged aluminum arm/spider design with an integrated bottom-bracket spindle for improved power transfer 4-arm 64/104mm BCD with aluminum outer, and steel middle/inner SG-X chainrings with pins/ramps for precise shifting Included SM-BB51 wide-stance bottom bracket cupset with outboard bearings offers increased rigidity (BB92 and BB30 adapter bearings available separately) Designed for a 50.0mm chainline and 135mm hub/frame spacing 995g with rings and BB @ 175mm