Unicel 4CH-950 Replacement Filter Cartridge for 25 Square Foot Top Load, Dimension One Spas Diameter: 4 5/8-inch; length: 12-inch Top end cap: semi-circular handle, 0-inch inner diameter; bottom end cap: 1-1/4-inch sae thread, 0-inch inner diameter Pleat count: 139; filter media: 3-ounce reemay 2033; filter area: 25 square feet Get more efficient filtration and better water clarity with Unicel filters Longer time between cleanings; meets oem specifications