This thermistor probe is designed to use with Pentair MiniMax NT STD, NT LN, NT TSI pool and spa heater models 200, 250, 300, 400 and also compatible with UltraTemp and ThermalFlo pool and spa heat pumps. Measures 1-inch length by 2-inch height by 1-inch width.  The probe is not in retail packaging as my supply was ordered in bulk.  It is brand new however and will be shipped in a bubble wrapper package with extra bubble wrap around the probe.  Please contact me with any questions.