This Replacement filter cartridge has a molded con handle on the top and a hole of 1 15/16 inch at the bottom. With 5 3/16 inch width and 11 7/8 inch length, the replacement filter cartridge can be used in 22 square feet Advanced Spa Design (original) and LA Spas. Manufactured with the technical specifications that complies with OEM# C5621 and thus, can easily replace Filbur# FC-3091 and Unicel# C-5621.