The pre-flashed, pre-assembled mounts are manufactured of fiber cement with an ABS flange. Providing a water management solution, blocks are easy-to-install and provide a clean finished look. To be used on standard lights and dryer vents. 8-1/2" x 11". No. 3SMU811AW4: Surface Dimensions: 8-1/2" x 11", Round Knockout: 3.625" diameter, Material: Fiber Cement, Color: Artic White No. 3SMU811P4: Surface Dimensions: 8-1/2" x 11", Round Knockout: 3.625" diameter, Material: Fiber Cement, Color: Primed