1/4" Compression X 1/2" MNPT Bored Through fitting. Includes a pair of silicone o-rings to make a liquid-tight non-permanent connection. This is the most popular compression fitting we sell and is used to adapt a 1/4" temperature sensor or probe into a 1/2" FPT coupler or weldless fitting.

I recommend using both o-rings as shown below.  The compression ferrule is not used when using the o-rings, it is only included in case you want to make a permanent connection.  The ferrule can also be crimped onto the tip of your probe to prevent it from being accidentally removed.  If you are going to use the fitting to crimp the ferrule in place, be sure to use anti-seize on the threads of the compression nut to avoid galling and damaging them.

Never make depth adjustments when there is hot liquid in the vessel!