This Replacement Filter Cartridge has replaces Unicel # C-4310, Pleatco # PWW10, Filbur # FC-3077 and has OEM # 378900 as other specification. It is 10 sq ft replacement filters for the following oem's skim filter and is best fit for Superior Spas, US Tooling & Spa, Leisure Bay Spas, Arctic Spas, Blue Fall Mfg, Charisma, Diamante Spas, Starlight Spas, Sonoma Spas, PDC Spas, Rec Warehouse, Thermo Spas of Connecticut, Weslo Spas, Accent Spas, Waterway Plastics, Hollibaugh Spas, etc. It has 2 1/16 inch hole at its bottom while 2 1/16 inch hole its top. This 4 inch long and 4 ¼ inch wide replacement filter cartridge provides you clear and pure water for swimming pool and spas. It is easy to replace without any hassle.