6061 aluminum hub shell with Centerlock disc brake mount 6al4v Titanium freehub body 11 speed (9/10 speed compatible when used with included spacer - except XD) High quality sealed bearings resist contamination Durable chromoly axles XD models are XDR compatible with included spacer RR 8-11s Cass 32H 12TA AL6061 Blk 265 CL 142mm 45 55 33 19