BestAir Pro SG411 Aprilaire 413 Replacement Air Filter, Fits 413/1410/2410/3410 and 4400 (Pack of 2) Nominal Size: 16 x 27 x 4 Actual Size: 16 x 27 x 4 Easy Installation Captures harmful particles in air; collects dust, pollen, dust mites, mold & spores Made in the U.S.A