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.