Limit Thermostat, Four (4) Terminal - SPDT - - Auto Reset - Open On Rise, (240-40F) - 240F and below the electrical circuit will remain closed, 280F and up will open the electrical circuit,  thus 40 degree differential.  For use on furnaces, dryers, fans, dishwashers, limits, ect., U.L.Rated, #SD240. These limit thermostats are brand new and made by Smart Electric Corp.