The ND series of Ultra-Zone dampers was designed with the installer and homeowner in mind. This damper is easy to install and easy to checkout. The LED display allows the installer to visually check the damper operation. With a sturdier frame, the damper installs in the duct much faster and easier and the nylon bushings insure quieter operation. This is a feature that homeowners will never hear about! Quieter operation and a longer life motor equals NO call backs.