These types of thermometers are development for industrial applications. Case, ring and stem are made of stainless steel.
low cost brass version.
They are available in a variety of temperature ranges, stem lengths & orientations, (any angle or straight rear), dial sizes & process connection threads.
The main use for those bimetal temperature gauges are in the heating industry. The thermometers are special designs are available for measuring waste gas, with display ranges of 0…400 °C and 0…500 °C, coloured control panels and drag pointers. A plain stem with magnet, tapered thread, or without thread, serves as a process connection.