Thermocouple GA183 or 110186-01 or 110183-01 33"
This thermocouple is 33" in length. It was used primiarily in unvented gas heaters.
When you let go of the button on the gas valve and the heater won't ignite, three parts may cause this problem. The thermocouple, the valve itself and a heat limit switch if your heater has one. Of these three parts, about 80% of the time its a bad thermocouple causing the problem.
Brands include: Comfort Glow, Vanguard and more
There are three different part numbers used for the same part-
GA183 thermocouple kit