Filtrete Dust Reduction Heating And Air Conditioning Filter. High Air Flow Filter Performs Better Than Ordinary Fiberglass And Washable 1" Filters. Electrostatically Charged Fibers Attract And Capture Large Airborne Allergens Like Pollen, Household Dust, And Lint. Ideal For High Velocity Heating And Cooling Systems. Microparticle Performance Rating Of 300. Lasts Up To 3 Months. No. 320Dc-6: 12 X 24 X 1 No. 305Dc-6: 14 X 20 X 1 No. 323Dc-6: 14 X 24 X 1 No. 304Dc-6: 14 X 25 X 1 No. 324Dc-6: 14 X 30 X 1 No. 300Dc-6: 16 X 20 X 1 No. 301Dc-6: 16 X 25 X 1 No. 302Dc-6: 20 X 20 X 1 No. 303Dc-6: 20 X 25 X 1 No. 322Dc-6: 20 X 30 X 1