Door grilles DO have a special design with 1 row of fixed Λ-shaped blades, parallel to the 1st dimension, which offers zero visibility between 2 adjacent spaces. They are suitable for use in air-conditioning and ventilation systems and wall or door instalation, for air transport (supply or exhaust) between 2 adjacent spaces.
Door grilles DO can be manufactured from anodized aluminium, aluminium painted in RAL color, from galvanized or stainless steel and copper :
DO... : Blades & frame from anodized aluminium or aluminium painted in RAL color.
DO... | C : Blades & frame from copper.
DO... | GL : Blades & frame from galvanized steel.
DO... | I : Blades & frame from stainless steel.