A look at how capillary thermostats work and how to use them.

Capillary thermostats are a simple electromechanical thermal switch that uses a very thin metal tube to sense temperature at another location, by using the thermal expansion/contraction of liquid or gas to activate an adjustable switch.

The search keywords for finding a wide range of units on eBay are:
"refrigerator thermostat"
Note that there are quite a few similar looking versions and a massive price range for the same thing.

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