Prompt Set Portable Spa Replacement Filter Cartridge, Pack of 4 Cartridges, Fits Prompt Set Classic & Deluxe Inflatable Air Bubble Massage Hot Tub in Box Prompt Set Portable Spa Replacement Filter; Pack of 4 Cartridges 4-1/3-Inch (4.3-inch) Outer Diameter by 3-3/4-inch (3.7-inch) Tall with 2-inch Open Hole on Top and Bottom Fits Prompt Set Portable Classic and Deluxe Models; for 600-Gallon/Hour Filter Pump