The filter frame is made from an anodized extruded aluminium profile with two angles in each corner to get a rigid straight frame. The zinc coated hood has an attached collar and is tie glued on top of the filter. At the damper (version A) the aerosol / pressure drop checking inlet is placed in a special middle bridge and is adjustable from downstream. The fibreglass media, which is pleated in ’Minipleat shape,’ is available in three different heights (47, 56 and 70 mm) and is cast into the frame and middle bridge. This design gives a highly active filter surface and ensures the minimal pressure drop of the GT model.