Unicel 5CH-45 Replacement Filter Cartridge for 45 Square Foot Freeflow Spas Legend Diameter: 5 5/16-inch; length: 10-inch Top end cap: open, 2-1/8-inch inner diameter; bottom end cap: 1-1/2-inch male thread/mpt, 0-inch inner diameter Pleat count: 225; filter media: 3-ounce reemay 2033; filter area: 45 square feet Get more efficient filtration and better water clarity with Unicel filters Longer time between cleanings; meets oem specifications