From the product description, check product page for current description, price and availability:

• MONITOR FERMENTATION: The G. Francis® Homebrew 1/4″ Stainless Steel Thermowell and #7 Bung Stopper for Glass Carboy Fermentation Temperature Thermometer Probe gives your temperature controller accurate readings to keep your beer at a precise temperature for sterile temperature control; Heating kit and carboy not included
• KEEP OUT CONTAMINATION: Place a probe inside the tube and then inside your beer fermentation vessel (not included) to monitor your wort while keeping out harmful contaminants and aeration
• USE YOUR CARBOY: Compatible with most standard glass carboys, temperature controllers, and airlocks; The thermowell is entirely removable from the stopper to fit different sized configurations (#10 stoppers are recommended for plastic carboys)
• COMBINATION SET: In addition to the thermowell, the included #7 bung plug stopper has an airlock hole with a 0.25-inch (6mm) diameter for standard size airlock to prevent your carboy from building up pressure; The stopper has a 1.3-inch (33mm) top diameter and 0.9-inch (24mm) bottom diameter and includes all hardware needed for exact temperature control even in colder environments
• SECURE FIT: Constructed with a stainless-steel tube and silicone bung stopper; Make sure the carboy surface and the stopper itself are dry in order for it to stay secure once pressed into carboy; Approximate 0.25-inch (6mm) tube inside diameter (ID); 15.5-inch (39.4cm) overall length; 14.25-inch (36.2cm) tube and 1.1-inch (2.8cm) stopper