Byson Air Grille, Plastic - 4" x 18"Byson Air Vent Grille White Plastic Rectangle 4. 3 inch x 18 inch (110 cm x 460 cm) with Screen Air vent grilles are designed for ventilation inside and outside of the building. Ventilation grilles are used to terminate ventilation ducts The advantage is the possibility to cover the vent hole of any size since, it does not have a back frame High quality ABS plastic. The grille has no flange. All models are fitted with screens. 4 Screw Cover Caps.