The HB-10-5W cartridge filter is a nominally rated “Calypso Blue Premium Grade” filter manufactured by Harmsco Filtration. The filter is 4.5″ in diameter and has a particle retention rating of 5 microns. The filter is 9.75″ in length and has 12 sq. ft. of NSF 62 Certified Polyester Cellulose filter media. This filter is a double open end, (DOE) configuration. Filters are individually wrapped in cases of 8.