Are all thermocouples created equal?

I have a trailer house furnace and the thermocouple apparently is going bad because the pilot goes out once every week or two. It just started doing that this fall, after the pilot was off all summer. I was at a local building supply and saw they sell a packaged thermocouple, but it does not specify what its for. Are all thermocouples created equal? I mean, can they be used for ANY furnace, or water heater, or any gas appliance? I am hoping so, because I dont know where I'd get one specific to this older Miller (mobile home) furnace.
PS. If I could figure out how, I'd convert it to electronic ignition, but that seems like a big job.
Thanks
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This is Turtle.
i will use the words of what type thermocouples are loosely to say the least. ALL per say 24 volt thermocouples will work in all applications just fine. Now there is a difference in the types of thermocouples that you may buy on at stores 7 wearhouses today. all will work but some are made to last longer and some is made to put out just a little more mill Volts for the gas valve to hold it open.
The HVAC type is made to put out about 27 to 29 Mill-volts and then the Hot water tank type is made to put out 24 to 27 Mill-volts service. anything 24 volts or over will work fine but the higher volt thermocouples seem to last longer.
TURTLE
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No, all thermocouples are not the same, there are many different types, J,K,T,R,S, and so one. The difference is the materials used for the wires. There must be 2 dissimilar metals for the junction to produce a voltage. Some use iron/constintan, others use copper/ cupronickel, others use different metals. They have different outputs at the same temperatures and are not interchangeable. Most Tc's for home use will be either J or K, and of those most should be J. You can tell by the wire insulation colors. J is red and white, K is red and yellow. Red is negative. As long as your wire color on the old one matches the new one it will be ok.
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Also, the millivolts is not what opens and closes the gas valve, that is just the signal to the temp controller telling it whether or not to open the valve. There is no voltage applied to a TC, so the notion that a TC is 24 volts or any other volts is wrong. The TC is an output device, not an input. The temp at the junction produces the millivolt signal.
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