If you want to install a dial thermometer in a double wall cooler, you'll need
an extended bulkhead like these. Here's how they work: The dial thermometer threads
directly into the open end of the coupling. The coupling extends through
the outside wall and insulation of the cooler and then the weldless
bushing/gasket seals to the interior wall of the cooler. This 1/4" NPT
version requires a 3/4" hole in the outside wall of the cooler and a 1/2" hole in the interior wall. The weldless bushing piece in this assembly is custom machined just for us so this isn't something that can be easily made from "off the shelf" parts.
Keep in mind that this bulkhead is NOT meant for draining liquid out of your cooler.
The picture below shows the application of this bulkhead for use with a dial thermometer. The picture shows both available sizes. BE VERY CAREFUL WITH THE SIZES OF HOLES REQUIRED ON THE INSIDE AND OUTSIDE WALLS OF THE COOLER.