• Outside Diameter: Measure either end-cap from outer edge to outer edge. NOTE: On the product specifications tables, the outside diameter will be found in the "Diameter" column.
• Inside Diameter: If either end-cap has an opening in the center, measure from inner edge to inner edge of that end-cap. NOTE: On the product specifications tables, columns "Top" and "Bottom" refer to the top inside diameter and bottom inside diameter, respectively.

Step 2: What’s the Length?

• Measure from the top edge of one end-cap to the bottom edge of the other.
• Do not include handles or other end-cap attachments in your measurement.

Step 3: Who Manufactured Your Filter?

• Determine the manufacturer of the filter from which the cartridge came. The Manufacturer may also be referred to as the OEM or Original Equipment Manufacturer. This information can generally be found either on a label affixed to the side of your pool filter or in the User's Manual that came with your filter.

Step 4: What’s the Model Number?

• The model number should be engraved on one or both of the cartridge’s end-caps.
• If there are several model numbers imprinted on your end-cap, match up the measurements you obtained in steps 1 & 2 with the appropriate model number listed on the end-cap(s).