Mavic makes swappable freehub bodies for most of their rear wheels so you're not permanently married to either SRAM/Shimano or Campy. You can start off with one body with its unique splines, and you can switch to the other fast. The bodies are known in Mavic-speak as FTS-L, or Force Transfer System-Light. The body is made of steel, as you'll currently find on all of Mavic's road wheelsets. In the recent past, most have had the FTS-L as well, save the Aksium. The M-10 is the Shimano/SRAM-compatible body. The Campy-spline version is known as ED-11 aka Campagnolo-11. ED-11 is the ED-10, just with the addition of a . 55mm spacer that slides onto the cassette body and nestles on flange at the spoke end of the cassette, so it sits between the cassette body flange and the tallest cog of the cassette. If you're still running Campy 10-speed, you just take the spacer off before installing your cassette. Campagnolo released their 11-speed groups without tipping off wheel manufacturers, so the manufacturers had to scramble. This spacer moves the cogs out ever so slightly. It's enough for all of the wheels Mavic has produced since February 2009, and most of the wheels before then. There are a few exceptions. The early Cosmic Carbone SLs, those produced before February 2009, have too bulky a drive side flange to work with Campy 11. The Mavic R-Sys and R-Sys Premiums produced before winter 2008-2009 also have too-bulky a drive side flange. In both cases, the new flange design is a bit narrower to accommodate that 11th cog.