This Replacement filter cartridge replaces Unicel # C-8380 and Filbur # FC-2810 and meets the OEM # 6540-401 specifications. It has 2 ½ inch hole at the bottom while 2 inch at the top. It is able to handle the top load of 80 square foot and is best fit for Sundance Spas – MicroClean. You get clean and clear water for your spas by installing this filter cartridge. It is very easy to install filter and made of superior quality of material.