Also known as snap discs, these thermostats switch on cooling systems or switch off heating systems when equipment gets too hot. Each thermostat has five temperature options for switch activation; choose the one that best suits your application.

Unlike heat-actuated switches, these thermostats reset automatically, saving you the effort of replacing a melted fusible link. To calculate their reset temperature, subtract their differential temperature from the temperature you set them at. For example, a thermostat set at 100° F with a 20° F differential will reset at 80° F.

Normally open thermostats are also known as low-limit thermostats—they turn on at a set temperature. They’re good for use with fans and blowers.

Normally closed thermostats are also known as high-limit thermostats—they turn off at a set temperature. They’re often used with electric water heaters, stoves, and furnaces.