Aftermarket Rims---caution!

I swapped out my Blizzaks on my 2010 last week. They'd been mounted on Konig Beyonds for winter driving, and I went back to my stock 3-season 19" Ford mags. I noticed that there was a black plastic ring needed with the Konigs to center the hub of the rim. Tire guy told me Ford rims didn't need these, but the Konigs did---and here's the caution----if I'd left these rings on & tightened the Ford rims with them still in place, thereby crushing them, there'd be a danger of the rims coming loose. I'd think these rings would be unnecessary because the lug nut would make the rim concentric, but the tire guy said this wasn't so. So if you swap back & forth---be aware. Incidentally---the dealer said the rims need tightening to 85lbs. of torque.

So---torque aside---and 85lbs is what my dealer said for Ford, our Volvo is 105lbs---what about the centering rings---that's my question---haven't any of you got aftermarket rims?

I guess I need a lesson in lug nut nomenclature---what's shank-style & acorn type mean?
And which describes the rounded ends the Mustang comes with?
The dealer insisted I buy separate lugs for the Konigs, and I did, but they look the same to me. Both have rounded ends where they seat---the only difference I can see is the Ford lugs fasten w/a 13/16" socket, while the aftermarket requires a 3/4" socket