TrueZONE ARD Series DampersFeatures: Adjustable close position range stops Shipped as power closed/spring return open damper. Available in 5 to 10" inch, 12, 14, 16, 18, and 20 inch diameter sizes. Male (crimped) and female (uncrimped) ends to connect to any rigid or flexible round duct. Rated to operate up to 1 in. wc Blade closes off tightly against gasket for minimal leakage. Fail-safe, normally open operation Simple, easy-to-wire, two-wire installation with a third wire option M4 for LED open only light