Originally Posted by Surly

One other note regarding the Fixxer: as I said, it is designed to work on most Shimano hubs. This does not just mean Shimano compatible hubs, as that refers to how the cogs fit on the freehub body. The Fixxer replaces the entire freehub body, and the way this connects to the hub itself is specific to each brand of hub. Spinergy, Zipp, etc. generally will not accept the Fixxer.