Used on Maxitrol modulating vent free gas valves. Buck Stoves used this valve in the past on some of their vent free gas fireplaces notably the Buck models, BR10, 1127, 34 and 327 with the modulating valve. Modulating valve means that the unit has its own thermostat built into the gas valve, there is a copper wire with a copper bulb on the end coming off the gas valve and this sensor controls teh on and off of the valve. The threaded end of the thermocouple is rather fine threaded going into the gas valve. Look at the threads carefully.
The photo below shows the type of pilot assembly this thermocouple is used in and how it is attached. When ordering you will get only the thermocouple.
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