Weldless Bulkhead | Compression Fitting 1.5 in. T.C.

This product does exactly what it looks like, and is well manufactured, but I have three caveats: 1) This thing has such a big radius that you'll need to mount it to a basically flat surface; 2) I pounded a curved portion of my kettle flat by hand, but even then I needed a beefier silicone gasket to get a good seal, so again, see (1); 3) most step bits aren't big enough to make the hole, so you'll need either a circular bit, or a Dremel and a skilled hand

But it does work brilliantly, and you can fit elements through it no problem, so if the above notes don't bother you, rock and roll