you mean like this?
ProVari Pro-Ring | Loki Lab
the "purpose" of them, is to give the device the look of a one piece hybrid. If you get the right size atty or tank, which is 22mm I believe, with a ring, it will look like one piece, sortof.
Like, a Silver provari, with a brushed ring and a brushed Kayfun 3.1, THAT will look like a hybrid.
But mine, a black provari, with a polished ring, and a stainless tank or polished Aga-T2, obviously isn't one piece, but it has the clean flush one piece look.
There is also the air flow rings, which arent just for aesthetics, they allow you to flush mount whatever topper you're using, and have control over the airflow by way of turning the ring to open or close the air path.(as opposed to having a slight gap, or slits cut in the device itself)