The UNI air filter is the best air filter on earth which is why it is used by the top names in racing. This filter can be washed and reoiled for continued use. A properly cared for UNI air filter will out last your engine! This is a dual layer foam filter. The red outer layer slips off easily for cleaning. The filter is 4"OD x 4"long. The mounting flange ID is available in 1 1/2" (fits 22mm Mikuni), 1 3/4" (fits 26mm Mikuni), 2 1/4" (fits 32mm Mikuni) & 2 7/16" (fits air filter adaptors) .