Cartridge Filter Systems come in a variety of styles. There are four industry standard cartridge sizes; 10" and 20" length and 2 1/2" (slimline) and 4 1/2 or 4 5/8" Big Blue. 10" filters are usually 9 7/8" and not 10" to add some confusion to the puzzle.

Some manufacturers make their filter systems take a proprietary cartridge such as Cuno and Everpure. There can be advantages such as a quick filter changeout or sanitary o-ring style connections but the cost for the cartridges can be higher also.