Expo stem-type thermostats are very accurate thermostats. These are specially designed for controlling the temperature of geysers, oil and water baths, sterilizers, air ducts, etc. Stem-type thermostat operates by opening and closing a snap-action switch in the load circuit. It consists of a brass tubing which is the sensor for operating and as soon as the particular temperature is reached the switch opens and thus switched off the main supply to the load.

When the temperature at the brass tube falls below a certain level the switch makes the contact and the main supply to the element is restored. In this way, the temperature can be set by adjusting the screw. The stem-type thermostat consists of a long brass tube with a switching mechanism on one side. The switching mechanism is placed inside a highly insulating and electrical-resistant phenolic cover. The temperature marking is done on a dial plate. The screw with the arrow mark can be adjusted as per requirement.