Amazon.com : SLSM for Bestway Type I Pool Filter Cartridge, High-Efficiency Filter Elements, 530 Gallon Pump Filter Cartridge for Pool Cleaning (3.11 x 3.54 inches) : Garden & Outdoor
Amazon.com : Bestway Size I Filter Cartridge for Pools, Blue/White, 3.1 x 3.5 Inch, Twin Pack : Garden & Outdoor