HAPF96 Holmes Air Purifier Carbon Pre Filter (Aftermarket) Fits Holmes room air cleaners HAP-560, HAP-570, HAP5604, and WAP-5600. 2 carbon pre-filters per box. Measures approximately 9 1/2" x 17 1/2". For optimum performance, replace pre-filter every 2 to 3 months. This is an aftermarket filter.