The 921-50 cartridge filter is a nominally rated “801 Premium” filter manufactured by Harmsco Filtration. The filter is 2.75″ in diameter and has a particle retention rating of 50 microns . The filter is 19.5″ in length and has NSF 61 Certified Polyester Cellulose filter media. This filter is a double open end, (DOE) configuration. Filters are bulk packed in cases of 24.