A/20K-BP - The ACI bullet sensor sensing element is double encapsulated to avoid sensor failures caused by moisture infiltration.  They are offered standard with etched Teflon lead wires. 

20K Ohm 1" Thermistor

A/20K-D-12"-BB - 20K Ohms @ 77 Deg F (25 Deg C) Thermistor The metal bell box (BB) configuration has a NEMA 3R rating and is designed for wet environments. The sensing element is double encapsulated to avoid sensor failures caused by moisture infiltration. ACI duct temperature sensors are designed for HVAC Building Automation and light industrial systems. Specific applications include: zone control air handling unit and temperature monitoring. Negative temperature coeffient double encapsulated sensor Built in mounting flange NEMA 3R enclosure