Glasfloss Industries HWR203042PK Z-Line Series 400 HWR MERV 10 Air Cleaner Replacement Filter Option, 2-Case Replacement option for Honeywell FC-40R Fits in most wall or ceiling return air grills with a 3 7/8" duct depth opening MERV 10 Performance Made in the USA Heavy Duty Moisture-Resistant Construction (Honeywell is a registered trademark of Honeywell Products, Inc.)