CLASSIFICATION AMT Grilles with moveable parallel bladesin the larger size.BMT Grilles with moveable parallel bladesin the smaller size. ADDITIONAL ACCESSORIES MATERIAL AMT-AN Extruded aluminium grilles.AMT-N Galvanised steel grilles.All grilles are provided with a seal on theback of the frame in order that the perimeter in contact with walls, ceiling, ducts, etc... is airtight. SP Opposed blades damper to regulatethe air flow. The damper is operated by an easily accessible key inside the grille. Constructed from electro-zinc steel, painted in black colour. The damper is held in place by SӔ springs.SPM-A...