Abstract: A rotatable knob for adjusting the temperature setting of a thermostat has a deformable tab that is permanently deformed upon rotational movement of the knob to a position that is indicative of a temperature setting greater than a predetermined optimum temperature setting. A deformed tab demonstrates that the knob was moved to a position for setting the thermostat at a temperature greater than the optimum temperature setting.

Abstract: A temperature sensitive normally open electrical switching device has a pair of normally isolated current carrying leads. A casing defines a central cavity and encloses first and second electrodes which are electrically connected to separate ones of the leads. An electrically conductive, fusible pellet is positioned in the cavity and melts at predetermined temperature to form an electrically conductive path between the electrodes. A spring and a nonconductive spacer apply a force to the pellet which will cause the pellet to collapse once the pellet material is fused regardless of the formation of an oxide layer on the pellet surface.