The sink has an opening that is just under 2 inches... yet the drain that fits into it says it is for a 2 1/2 inch hole.

When researching other sink drains (made with actual 304 SS) I see that they are made to fit 2 1/16, 2 7/16, and 1 1/2in drains and 2 1/2 inch drains along with some other odd designations... depending on the manufacture and how they choose to label their product.

Without actually fitting one of these things into place, I have no idea what the numbers mean... even while looking at their somewhat more "detailed" specification drawings.

I do feel better about NPT and various bronze fittings and tailpieces... at least from Groco... they seem to be speaking the same language at least at that one company.

Now bronze and "red brass" oh boy, don't get me started.