Pre-Filter (51906) Protects Oil & Dry FiltersFor Usewith Oiled Filters #5111, #5119, #5150, # 5161, and Dry Filter5160 Volant Pre Filters are factory treated using a proprietary hydrophobic process and are manufactured from the same durable polyester material as their race proven regular style. This unique material contains uniform micron openings that will filter out debris . 005 or larger. This pre filter will prevent splashes of water, mud and sand from saturating your air filter.