Do you want to monitor the temperature of your 5 or 10 gallon Igloo or Rubbermaid (and Home Depot) cooler while you are mashing or storing sparge water? The Coolview™ thermometer from Brewer's Edge®, features a cooler-specific 100° to 200° F. Range, and a sliding red reference pointer so you can set it at mash or sparge water temperature. The 2" dial features a calibration nut for fine tuning the temperature if desired, as well as a unique 1 3/4" long threaded stainless barrel that is 5/16" thick, so it can be installed in thick cooler walls by just drilling a 5/16" hole. Click on the More Info link above to see a photo of the back of this thermometer.
To prevent leaks into the cooler wall foam insulation, a specially designed mounting nut features a machined recess to hold a small silicone O ring. This recess holds the O ring tight in the nut when you tighten the backnut, preventing it from spreading and causing leaks. A great aid if you have a cooler mashtun or sparge water tank.
Click 
here to view Coolview installation instructions.
This shows the back of the Coolview, with its overall 3 3/4" length and backnut with silicone O ring. To adjust the calibration, the nut at the base of the stem is turned with a small wrench. Installs in any 5 or 10 gallon insulated cooler once you drill a 5/16" hole.
You can be the first to ask a questions.
Very cheap and flimsy
If your hole is not perfectly square through the cooler insulation it will leak because the seal is super thin. The gauges themselves are not very sturdy. The way they are calibrated is by turning the outside cover relative to the body. If it gets bumped at all the temperature will need to be calibrated during the brew process which is not easy to do while you are brewing. I end up buying some much more robust thermometers on xxx. I would recommend these.
NOT Accurate. Cheaply made!
As others have mentioned, it's easy to knock the thermometer out of calibration. The point of buying 2 of these....one for sparge tank and one for mash tun, was to cut down on brew time and limit variables. Now, I have to make sure each thermometer is calibrated before I begin a brew and I remain paranoid during mashing/sparging. Waste of time and money.
Nice Fit
Product sealed really well on 10 gallon igloo mash tun. Dial was accurate and true, but be sure to place it close to the bottom. For some 5 gallon all grain batches it needs to be fairly low on the cooler to get a good reading...and once you drill the hole, your done.
Worked well for a while, but now it's dead.
This product was easy to install and fit perfectly in my mash tun. It only lasted less than a year... now I am looking for another one. :(
Easy to install, works as advertised
Easy to install, had a small initial leak that was quickly and easily corrected. Seems to be very accurate. Nice, inexpensive addition to my rig that should improve my beer.