The Unicel C-5637 R is a replacement spa filter that is the correct replacement for the following filters:
The Unicel C-5637 Comp. Pool Water Filter Cartridge has a diameter of 5 3/16 inches, and a length of 19 5/8 inches. This Unicel spa filter has an open top with a diameter of 1 1/16 inches, and an open bottom with a diameter of 1 5/8 inches. This pool filter cartridge contains 40 square feet of 4 ounce filter media.