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