Construction: Louver: Z-blade louver is riveted to the operating bar and frame at 1″ intervals to welded 1-9/16″ deep frame. Mechanical Stop holds blades open. Frame: Mitered and welded corners: screws fastened through prepared frame into louver core leaving corridor side of frame free of fasteners. Operation: Adjustable blades of 16 gauge CRS pivot on cadmium-plated steel rivets. The blades are operated by a manual adjusting lever. A spring loaded fusible link mechanism is incorporated into the design; upon melting of the link, the action bar is actuated, thereby closing and locking all of the blades. Door: For- 1-3/4″ steel or composite door. Door cutout = order size. Fasteners: #8 x 3/4″ Phillips flathead screws to match finish.