GSW DF-18S 18-Inch Stainless Steel 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 304 stainless steel. 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