The Kuryakyn Skull Air Cleaner kit is not for those who are weak in the knees and they make a seriously sinister addition to the right kind of Harley Davidson. The outer cover is basically the same cover used on the S&S carb cover with some sinister modifications. These kits also include a backing plate and high-flow K&N filter element as well as all of the necessary brackets, crankcase breathers or hardware required for a quick and easy installation.