Dial thermometers are made with galvanized steel housin […]
Dial thermometers are made with galvanized steel housings while the lids are made of a material resistant to scratching. The measuring device is based on a bimetallic spiral.
Dial thermometers employ either a bimetal or gas expansion mechanism. The first takes advantage of the different linear expansion and contraction rates of two strips of dissimilar metals laminated together.
One end of this assembly is attached to the needle. As the temperature changes, the strip bends, causing the needle to move.