Oil filters help remove impurities in your oil system that come in through the air line. Your oil flooded air end is constantly cycling through the oil in your sump tank. Each pass through the oil filters ensure as much of the impurities are removed as possible and produce cleaner air down line. Air Compressor Services' 6.4778.0 oil filter is the ideal part to replace your Kaeser branded oil filter part number 6.4778.0. Our oil filter is guaranteed to match the micron rating and usage life of the Kaeser branded filter.