Originally Posted by capwater

You should have 2 spacers: a thicker one which is required for all Mavic wheels in the 8/9/10 speed family and a thinner one which is neded for 10 speed shimano casettes. Bottom line is keep both spacers there and just replace the cassette. FYI, freewheel is not a term involved in this discussion; you have a casette which goes on a hub.