Mechanical High Limit Switch - 36" Capillary - 4" Probe (Sensor).
The capillary (probe wire) is 36" long and comes tightly wound. If you don't require the full 36 inches, simply leave it partially wound up.
High limit switches are a safety device that will open the circuit if your hot tub thermostat or contactor fails and the water reaches a very high temperature (usually about 120 ° F).
The open circuit will turn your heater off. It can be re-set by pressing the red button.