O.S. air filter elements have been pretreated with a special lubricant which traps fine dust particles and keeps them from damaging the engine. This reduces engine wear and assures reliable performance and longer engine life. This products includes one bell shape rubber mount. Three pretreated foam elements. This is used with the .12 size engines. Directly Fits: OS .12CZ-11, 12CZ-R, .12CZ-Z, .12CV