Standard construction Frame: 8"x11/4"x16ga. galvanized steel channel Flange: Corner 0.4" dia. x 8 EA for installation bolt holes. Blades: 22"Ga. galvanized steel upto 36" length. 22"Ga. galvanized steel upto 48" length Min blade dimension: 6" Linkage: Concealed in frame or face linkage inside of air stream. Bearings: sleeve bearing Axles: 1/2" dia. galvanized steel. MIN. Damper size: PB single blade-5" W x 4" H MAX. Section size: 48" x 72" MAX. damper size: 72" x 72" Steel construction: welded constructions Axles: bolted to blade and tag welded. Finish: Galvanized steel zinc plated hardware. Installation instruction Air flow rate control between duct and duct bolt conection Variations(at extra charge) 1. Special finish 2. Special material: alum., stainless steel, etc. 3. Special blade seals and axle shaft seals 4. Special thickness of blade or frame.