This Replacement filter cartridge has the technical specifications as Unicel # C-4440, Pletco # PSD40-4, Filbur # FC-2710 and OEM # 6540-495. This 16 ¾ inch long and 4 5/8 inch wide filter cartridge has 2 1/16 inch open hole at its bottom while a castle at the top. It is capable of handling the top load of 40 square foot and is best fit for Sundance Spas, Jacuzzi Spa Div. This high quality filter cartridge provides you complete protection from germs and sand in your spas and pools.