I use this as a replacement for the orange airlock shipped with the Speidel tanks. It gives me lots of options for closure or other accessories, like the inert gas system.

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 handBut 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