These are steel roof caps with a durable black finish. Use the 636 model to exhaust from 3 or 4 inch round ducts. Use the 634M model to exhaust from 6 inch round ducts. They have built-in backdraft dampers to prevent uncontrolled air infiltration, as well as bird screens.
Dimensions (636): 11" inches x 10.25" inches (plus flashing)
Dimensions (634M): 18.75" inches x 14.25" inches (plus flashing)
