SMP round dampers are designed to fit inside pipe sizes ranging from 6″ to 48″ round. The welded 2″ deep frame is undersized 1/4″ for ease of installation, the damper blades are a formed 16 gauge galvanized steel with linkage in the airstream for better blade operation. This damper has a 1/2″ round control rod that can be operated by either a hand quadrant with standoff or an actuator.