Kair 110 x 54mm Gravity Grille Vent Cover With Rectangular Spigot Square Plastic Air Inlet / Air Outlet with Gravity Shutters 110mm x 54mm rectangular spigot on the back of the grille fits inside the Kair 110mm x 54mm Rectangular Duct Pipe (Part: DUCVKC249). Non-return shutter flaps close automatically when not in use. Stops unpleasant odours, noises, or draughts flowing back through your duct.Gravity flap - no need for springs that break. Built to last out of high-quality Polystyrene/Polypropylene plastic Material.Max / Min Temperature: +60c / -15c. Wipe-clean durable design for indoor or outdoor use. Suitable to use in compliance with Part F Building Regulations.Airflow performance independently tested by BSRIA or BRE.Free Air: 5,800mm2.Static Pressure Drop in Pascals: 15 l/s = 4.81 Pa - 30 l/s = 15.71 Pa - 60 l/s = 51.40 Pa.