You haven't identified the gruppo as index or friction and I'm pretty sure you have a freewheel hub, not a freehub. Regardless Dura Ace 7 speed has a max cog of 26T. The freewheels are pripriatory and a little hard to come by but they are still out there..
Last edited by onespeedbiker; 05-14-12 at 11:26 AM.