This Mavic 60mm Alloy Valve Extender is just the thing for pairing with their line of aero wheels, like the Cosmic Carbone Ultimate. It looks similar to any other alloy valve extender, but Mavic gave it a special purpose. The inflation end has been designed to function as a tool to open and close the valve nut on your Presta valves deep inside the rim.
The benefit is that you can air up your tires and be sure that you won't have any slow air leaks from the valve. After all, Presta valves were designed to be as light as possible and to be easy to fill with a hand pump. An integral part of that design was the valve nut that must be closed to ensure a perfect seal. Otherwise, you'll rely on air pressure alone to hold the valve shut. Mavic designed the 60mm Alloy Valve Extender to be easy to install and remove by hand as both ends are lightly knurled to facilitate good grip. Each extender also comes with a complement of five O-rings (only one is used at a time and they're re-usable) that maintain a perfect seal on the valve stem.