I used an inch and seven-eights (1 7/8) bi-metal hole saw and then carefully made the hole larger a little at a time with my dremel tool checking for fit each time. I wanted the ferrule to fit tight into (not on top of) the side of the kettle. I then had a guy Tig weld the Ferrule and grind the inside smooth after. It turned out very nice. I'm sure there are many other methods out there, but this one worked for me. Good Luck. Just drill slow speed and steady with some cutting oil. It does go easier than you might think.
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