This thermocouple is an 18‑inch universal replacement designed for furnaces, water heaters, boilers, and gas space heaters. It’s made of copper (with universal fittings) so it can fit a wide variety of pilot burners — making installation relatively straightforward. The thermocouple produces a small millivolt signal (typically 18–30 mV) to indicate the presence of a pilot flame, which helps the gas valve stay open safely when flame is present. The universal design allows it  to be used as a direct replacement for various older thermocouples from different manufacturers, offering a practical, low‑cost way to restore safe operation when the original thermocouple fails.