This replacement filter cartridge replaces Unicel # C-4311, Pleatco # PDS45 and Filbur # FC-2394 while complies with the OEM # C4311 specifications. This 12 ¼ inch long and 4 15/16 inch wide filter cartridge has 2 1/8 inch open holes both at the top as well as bottom. It is capable of handling the top load of 45 square feet and the most suitable for Dakota Spas. It provides you complete protection from germs and and sand in your spas and you get clean and clear water. Very easy to install this filter cartridge is made of high quality materials.