400/405 Series thermostats are mercury free and environmentally safe. Their unique hermetically sealed-in-glass switch design requires no leveling and provides optimum protection from contamination. The basic 400/405 thermostat can be used as a heating only, cooling only, or zone system thermostat, depending upon how the subbase is wired. The 400/405 Series thermostats, when used with the 490/495 Series Universal Switching Subbase, will replace most heating/cooling applications. Decorative Wall Plate is included with all models. It can be used to cover old thermostat mounting marks.