Surly's Ultra New Disc Rear Hub is just the thing for singlespeed fanatics and one-gear mountain riders. This gorgeous hunk of aluminum boasts reliable sealed bearings and a 6-bolt disc attachment on one side and threads for a singlespeed freewheel (or fixed cog) on the other. A hollow axle lets you choose how to secure it to your dropouts. You have choice between the included fixing bolts or a quick release skewer (sold separately). And, that aforementioned chromoly axle is flex-free to take all the abuse you can dish out, and then some!