Unicel C-8465 Replacement Filter Cartridge for 65 Square Foot Hot Springs Spas/Watkins Mfg Diameter: 8 1/2-inch; length: 10 1/2-inch Top end cap: open, 3 0/0-inch inner diameter; bottom end cap: open, 3 0/0-inch inner diameter Pleat count: 234; filter media: 3-ounce reemay 2033; filter area: 65 square feet Get more efficient filtration and better water clarity with Unicel filters Longer time between cleanings; meets oem specifications