Thermowells keep the bad stuff away from the thermometer so that it has a long and happy service life.
Installed in a permanent position before the process begins, thermowells are usually one-piece designs which act as a second skin for thermometers.
The thermowell transfers the heat or cold from the medium being tested via a hollow tube which the thermometer fits into. The tube is closed at one end and the temperature testing equipment is inserted and removed from the other.
In many cases, a thermometer can be secured inside the thermowell with a threaded end.