This is a genuine OEM Hoover C2401 Commercial Backpack HEPA Filter cartridge assembly designed to fit Hoover part number 2KE2110000. This filter also fits Royal Commercial Backpack model RY4001. Located inside of the dust bin, this washable, rinsable pleated cartridge filter protects debris from entering the motor, and is very important to maintain frequently, washing every 30 days, and replacing once every year, to maintain peak cleaning performance, and ensure your motor is not overheatng while running. Some prefer to have two filters on hand to have a backup to use while waiting for one to air dry fully. It's imperative that you do not reuse the filter until it has fully dried, which can take up to 24 hours. Genuine Hoover C2401 / Royal RY4001 HEPA filter cartridge, part 2KE2110000.