Daisy Wheel for 4 inch Air Duct

This is a 4in daisy wheel that I am using to turn a 4 inch duct stopper into a controllable vent. After having trouble controlling the exhaust fan speed for my k40 laser cutter, I decided to make this to control the level of exhaust pressure by using this daisy wheel in a T-adapter to create a "leak" exhausting air from the room thereby lowering the pressure in the laser cutter. It is made for and M8 bolt at the center.