What material is the helical shaft made of in a fan/limit switch that reacts to temperature changes?

The helical shaft in a fan/limit switch that reacts to temperature changes is made of bi-metallic material. Bi-metal refers specifically to a component that consists of two different metals bonded together, which expands and contracts at different rates when subjected to temperature variations. This unique property allows the bi-metallic strip to bend or change shape in response to temperature fluctuations, thus enabling it to actuate the switch mechanism effectively.

As temperatures rise or fall, the bi-metal will respond accordingly, helping to regulate the operation of the furnace and ensure that it operates within safe temperature limits. This mechanism is critical for maintaining proper furnace function and preventing overheating or unsafe operating conditions.

In contrast, materials like stainless steel, plastic, or copper do not provide the same functionality for temperature-sensitive applications. While they may have their own uses in HVAC systems, they do not possess the desired properties for the thermal reactions needed in a fan/limit switch.