Unicel C-7370 Replacement Filter Cartridge for 75 Square Foot Sundance Spas Diameter: 7 1/2-inch; length: 17 3/4-inch Top end cap: castle, 0-inch inner diameter; bottom end cap: open with beveled edge, 2-1/2-inch inner diameter Pleat count: 154; filter media: 3-ounce reemay 2033; filter area: 75 square feet Get more efficient filtration and better water clarity with Unicel filters Longer time between cleanings; meets oem specifications