Truaire C168-OBU 18-Inch(Duct Opening Measurements) Solid Oak Floor Baseboard Supply 18-Inch Solid Oak Baseboard Diffuser, Unfinished High-grade solid oak Model Size Indicates Duct Opening Measurements not Wall Opening Measurements. High quality solid wood components Solid wood damper The actual face size is 18-inch in width and 2.75-inch in height.