NSD Outerwears Prefilter CoverUse with WCF100717 or WCF100719 These Pre filters contain uniform micron openings and are run dry meaning no additional oils or additives are required. Running a dry Pre filter means there is no dirt sticking to the oil creating premature loss of airflow and horsepower. Only those particles of dirt smaller than . 005" get into the actual air filter, the larger particles simply fall off the pre filter. In addition, these filter covers are constructed