... sensitive and effective shutter Made of galvanized steel ,Air Damper,Volume DamperWith sensitive and effective shutterBack drought shutter, one way shutter, shutter, damperSize:100, 125 ... sensitive and effective shutterBack drought shutter, one way shutter, shutter, damperSize:100, 125, 150, 160, 200, 250, 315 back draught damper / one way shutter / duct shutter