This would be a damper, perhaps installed behind a wall or floor-mounted register for a whole house hvac system. It would allow adjustment to the airflow into a given room and would effectively focus cooling or heating in the rooms that need it most, by limiting flow to rooms that are comfortable already.
Hi @dougc2000 .
Was this an answer to a lost question or just for educational purposes? I would hate for a user to miss your post if you were trying to help.