There are two Balboa M7 system heater sensors located at each end of your heater and are identical to each other. The most common sensor we do - This is a single M7 heater sensor. Hot Tub Chemicals.

Brand: Balboa
Type: Temp Sensor
Set Includes: 24 inch Sensor
Model: M7
MPN: 30382+
Item Length: 16-25 in (40.6-63.5cm)
Features: Easy Installation
Water Type: All Water Types
Manufacturer Warranty: 12 months