Pentair 471566 Thermistor Probe Replacement Pool/Spa Pump and Heater Distributor Packaging Fits Pentair MiniMax NT STD, NT LN, NT TSI pool and spa heater models 200, 250, 300, 400 Also fits UltraTemp and ThermalFlo pool and spa heat pumps Measures 1-inch length by 2-inch height by 1-inch width