Replacement Carbon Pre/Post filter made by Filter Everything and compatible with Holmes Air Purifiers HAP422 Series. Dimensions measure 1-1/4 x 9-1/2 x 1/4. Sold as a 6-Pack. Our filters are manuctured to meet or exceed OEM quality and are fully compatible with the name brand (OEM) model. Aluminum filters should be cleaned every 60-90 days; carbon filters should be replaced every 6-9 months. Proudly packed and shipped from our facility near Cleveland, OH.