The Filtrete 64821-4 is the correct replacement filter for the following models:
The Filtrete 64821 - Hoover T-Series Replacement HEPA is a vacuum filter for the Hoover WindTunnel T-Series Upright vacuum cleaners. This Hoover Vacuum filter features electrostatically charged fibers and HEPA media that trap 99.97% of airborne pollutants as small as 0.3 microns, including mold spores, pet dander, grass and ragweed pollen. Filtrete recommends that this WindTunnel filter be replaced every 90 to 120 days for the best air filtration results.
Filtrete 64821 - Hoover T-Series Replacement HEPA specifications: