COMPATIBILITY: MERV-13 Pre-Filter Replacement Set Compatible with Mounto AF500, Drieaz HEPA 500, BlueDri AS550 Air Scrubber. FEATURES? MERV-13 Pre- filters A MERV-13 pre-filter is the first filter airflow passes through. This filter filters the largest particles, allowing smaller ones to pass through. Pre-filters are generally changed the most frequently. PACKAGE: 5 X MERV-13 pre-filter This is not an OEM product. The brand names and logos are the registered trademarks of their respective owners. Any use of the brand name or model designation for this product is made solely for purposes of demonstrating compatibility.