The EBC Pro-lite X Series are 6 button ultra lightweight floating rotor for Sportbikes and Road Racers. The X Series features EBC's unique and patented S-Drive button system which features square sided rivets captured in square drive pockets on the rotor and hub which allow the outer rotor blade to expand and contract freely under the heat of braking without suffering rivet lock. This stops brake judder whilst ensuring the discs don't warp under heavy braking The Pro-lite X series are riveted together and are no longer rebuildable due to the infinite service life obtained with the SD square drive button system. The difference between the X Series and the XC series is that the XC series come with the funky contoured design.