Balboa Sensor Assembly
For older pressure switch Balboa systems.Single connector to the circuit board with two sensors, the larger  temperature 3/8 sensor goes into the spa and the smaller 1/4" high limit sensor goes into the heater back. If your reads 30288 or 30337 this is the sensor for you.

For your identification the cable label will read:
S/N 30337 SENSOR ASSY 96" (3/8, 31" (1/4)

Balboa Hi Limit sensor
This is a Balboa Hi Limit sensor for Balboa systems.
S/N 30298 SENSOR 31 inches length (Diameter. 1/4inches)

Balboa Temp sensor
Temperature Sensor, 96", 3/8" Diam (2-Pin Connect) - Balboa 30294

Balboa Heater M7 Sensor (most common in UK)
This is a single M7 heater Sensor. There are two Balboa M7 system heater sensors located at each end of your heater and are identical to each other. The length from the tip of the sensor to plug end is 24”- this comes as a kit complete (32016) includes washer & o-ring. Replaces sensors marked 30382 & 30344