K&N Engineering Universal Round Straight Air Filter - Rubber End Cap RU-0800When selecting one of K&Ns universal round straight air filters, you should consider the following dimensions as they relate to the specification chart: Mounting Flange Inside Diameter This is the most critical dimension and should be very close to the diameter of the applications inlet flange. The flange will stretch up to 1 8in. for those in between sizes. Filter Diameter This is the overall diameter of the filter. Always use the largest diameter