Pool Filter Replaces Unicel C-8465, Pleatco PWK45N, Filbur FC-3960 Filter Cartridge Swimming Pool Spa New unicel c-8465 65 sq. Ft. Watkins/hot springs spas replacement cartridge filter Outside diameter: 8-1/2" Length: 10-1/2" Top end cap: open, 3" inner diameter Bottom end cap: open, 3" inner diameter