Filter Cartridge For Sundance Spas MicroCleanTM I Filter System. * The MicroCleanTMcartridge provides maximum filtration for crystal-clear spa water. For use with Sundance 850 & 780 Series Spas. * The complete MicroCleanTM I Filter System pictured in insert is to help ensure you select the correct replacement filter. Each MicroCleanTM I Filter System component is sold separately. * The 6540-501 Sundance Spa MicroClean replacement is a OEM Factory Original * Approximately 14 Inches in length by 8 1/2 inches in diameter and has a closed top with SAE threads and a 2 1/2 inch opening on the bottom