When for some reason the previous owner hired an HVAC contractor to install his new and highly efficient system, he never installed mufflers in round tubes. They are expected to be installed after launch. Of course we have some stops that throw air into the room with such force that they whistle while others can barely move the candle flame! This leaves hot/cold zones (depending on the season) that cannot be compensated for. This tool allows you to cut a clean groove into which the damper can be installed. Now I can balance the system properly!