Limit Thermostat, Four (4) Terminal - SPDT - - Auto Reset - Normally Closed - Open On Rise, (190-20F) - 190F and below the electrical circuit will remain closed, 210F and up will open the electrical circuit,  thus 20 degree differential.  For use on furnaces, dryers, fans, dishwashers, limits, ect., U.L.Rated, #SD190-20. These limit thermostats are brand new and made by Smart Electric Corp.