The 450/455 Series Contractor Thermostats feature the same quality Robertshaw thermostats and subbases that are found in our 400 and 490 Series used in the 450 Series "no frills" contractor model. 450/455 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. Available as Wall Thermostat only, Subbase only, separately packaged Thermostat and Subbase (ideal for tract applications where installation is done in stages), or single package Thermostat and Subbase, the 450/455 Series will meet your needs ? and at a reasonable price.