GSW DF-18P 18-Inch White Powder Coated 4-Way Adjustable Metal Diffuser for Evaporative/Swamp Cooler This product is designed to cover a 18" x 18" hole size. The mounting size is 20" x 20". See image White powder coated metal. For evaporative/swamp cooler 4-way adjustable Body dimension: 18"W x 18"L x 6"H 1" width edge at the end of the body for easy installation