It is a great quality replacement filter cartridge that complies with the technical specifications as Unicel # C-8325, Pleatco # PSD125U and Filbur # FC-2790 and OEM # 6540-490. It is the most suitable for Sundance Spas and capable of handling the top load of 125 square foot. This 18 inch long and 8 7/16 inch wide filter cartridge has open hole of 2 ½ inch at its top while closed w/3 step edge at the bottom. By installing this filter cartridge you will get clean and clear water free from dust, sand and worms.