The quality you expect with the performance you need, so you can enjoy your pool worry-free. Dimensions and specifications of the cartridge. 3 ID Top and bottom (open hole) Nominal dimensions. 17-3/8″ L x 7″ OD x 3ID. End caps are both open with polyurethane material to provide high impact and perfect seal, our core is injection mold creating more stability than drilled PVC pipe. Hayward Swim Clear C2030, CX481XRE, CX481-XRE PA56L, PA56L-PAK4, PA56L-4, Unicel C-7456, PLFPA56L, Guardian 717-145. Cartridge meets OEM specifications. This Package contains 4 Cartridges.