Often used to control heat cable output, these switches mount on surfaces to maintain the temperature within a preset range. All are single pole, double throw (SPDT). They turn equipment on when the surface temperature falls below the minimum actuation point and turn equipment off when the surface temperature rises above the maximum actuation point. All are FM approved for use in Class I, Division 2, Groups A,B,C, and D hazardous locations with flammable gases, such as refineries and chemical plants.