Originally Posted by timcupery

All Shimano 9-speed cassettes will fit on all non-Dura-Ace 10-speed freehubs. Dura-Ace 10-speed is the only oddball here, because of the higher splines required to not strip since the freehub body is aluminum for light weight. Other than D/A 10-speed freehubs, all Shimano 8, 9 and 10-speed freehub bodies are compatible with all all Shimano 8, 9, and 10-speed cassettes. And of course, D/A 10-speed cassettes will fit on other Shimano freehubs.