I did not explain that very well.
You CAN attach copper or brass fittings directly to your stainless pot. It is not exactly easy, it is simple to get wrong, I have done it before and I would NOT do it again.
A far better option IMO is to cut a 5" or 6" hole in your stainless lid and fit a copper plate to cover it. You can rivet and solder if you like, or bolt it together with a safe gasket. Either way it is intended to be a permanent or semi-permanent fit. You have just converted your stainless pot into a hybrid copper/stainless one.
This was hard soldered onto the stainless bowl with 56% silver solder for a rock solid permanent joint. These days if I was to use a stainless pot I would fit a copper plate or bowl to it first.
All your still fittings are then attached to the copper plate which is REAL easy. Also way more versatile. You want a 4" opening into your pot still for cleaning? Working in copper it is no problem. If you want a 4" fitting that will cost you.
With a copper plate fitted you don't need ANY fittings to connect your pot still neck. You can flare copper tube and solder it onto the plate.
Not saying don't do it. This was an early thumper I built just to show that you can solder copper tube directly into stainless.
Just saying that I don't do it any more. Personally I prefer to build in copper and leave stainless to those that like to work in it.