The bimetal disc will snap at the appropriate temperature separating the electrical contacts. This particular model is a 1/2″ Snap Disc Thermostats.

The 431 series encapsulated 1/2″ Snap Disc Thermostats is used whenever a moisture and dust proof enclosure is required for safe, sensitive and reliable operation. A polypropylene boot enclosure, filled with epoxy resin, covers the thermostat. The bimetal disc control element is in close proximity to the sensor cap to provide rapid response to temperature changes. Since the bimetal disc used in the Type 431 thermostat is the1mally and electrically insulated from the cun-ent can-ying parts of the thermostat, the disc reacts only to the temperature of the controlled device or medium surrounding the disc. Instantaneous, positive action of the disc prolongs thermostat life by minimizing arcing and eliminates chattering, false cycling and electrical interference with radio and television reception. Long life is assured with wiping contacts.