Keep your pool water clean and clear with a Mainstays Pool Filter Cartridge (Type VII, Type D). This replacement pool filter cartridge measures 4.2 in x 3.8 in and is designed for filter pumps that utilize Type D cartridges. They are easy to clean and sift dirt and debris out of your pool with your pump. Bestway® recommends replacing them every 2 weeks for best results. These pool filters are great to use for keeping your pool clean, but they do not replace the need for regular chlorine maintenance. With filter cartridges and proper upkeep, your pool can last year after year!