Radiant Saunas BP570-4 Inflatable Spa Replacement Filter Cartridge, 4-Pack Fits radiant brand pinnacle and simplicity inflatable spa models Dimensions: 4-in diameter x 3-in h with threaded 2-in center hole Durable construction with extra pleats for improved filtration and water clarity Easy to clean and replace Recommended to clean after each usage and replace after 7-10 days of use