This carboy thermowell is used in conjunction with the digital thermostat to more accurately regulate internal temperature during fermentation. It is exceptionally useful during the start of fermentation when the lag between ambient temperature in the refrigerator and actual temperature in the carboy can vary greatly. Now you can keep your beer or wine within one degree of the set point on your digital controller. Designed to fit either the 5, 6 or 6.5 gallon glass carboys, or any other similarly sized opening hole, the unit comes with an 15' stainless steel thermowell and a 6.5 stopper. It can be used in any container with a stopper opening where you need to accurately monitor and control liquid temperature. You can use this with your refrigerator for exact cooling temps, or use it with one of our heating products to control how warm your fermenter gets.