Leakproof construction with machined gasket seat and UL listed gasket compounds. High quality wool felt filter elements that remove solid contaminants Iron and steel construction for maximum integrity and durability Low pressure drop, suitable for gravity flow and one or two pipe systems on pressure type burners Micronic filtration suited to the smallest oil burner nozzle Bonding treatment of center core in filter element eliminates lint. Step design element offers largest dirt capacity with true depth filtration Listed by Underwriters'' Laboratories.• The perfect fuel filter for oil fired heating appliances• Used in small to average sized homes and commercial buildings• It is ideal for final filtration in central fuel oil distribution systems• The 1A-25A may be used inone or two-pipe systems• 3/8" NPT standard.