Manufactured to order from 0.7mm or 0.9mm galvanised mild steel depending on size. Grille boxes are available with or without a 20mm flange at the open end. Most grilles require this flange; egg crate, single and double deflection for example are generally always screwed through the front face into the flange on the box. Diffusers however, do not require this flange as the boxes are commonly fixed to the grille through the side of the grille box.
Click on a size from the drop down menu below that represents dimension A in the drawing (dimension B can be selected on the following page).