The filter frame is made from anodized extruded aluminium profile with two angles in each corner to get a rigid straight frame. The zinc coated hood with an attached collar is tie glued on top of the housing. 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 filter frame and middle bridge. This design gives a highly active filter surface and ensures the minimal pressure drop of the HT model.