KI snap action thermostat is a small-sized bimetal thermostat series with a metal cap,which belongs to thermal relays' family. The main principle is that one function of bimetal discs is snap action under the change of sensing temperature. The snap action of disc can push the action of the contacts through the inside structure, then caused on or off the circuit finally. The main characteristics are the fixation of working temperature , the reliable snap action, less flashover , longer working life and less radio interference.