How to identify your pool and spa filter cartridge? Measure the outside diameter of the cartridge. Measure the overall length of the cartridge in inches (± 1/16), including the end caps. Do not include any handles, strings, etc. A more accurate measurement is made by measuring through the center of the cartridge when possible. If the top and/or bottom is open, measure the inside diameter of the opening (±1mm). If the end cap is closed make note of its identifying features i. Take note whether or not there is a center core. Also count the number of pleats (±2). Filtration Area: 105 sq. Package Quantity: 4 Filters. All manufacturers’ names and part numbers remain the property of their respective holder(s) and are used for compatibility information only.