i bought the pack of fondant rolling pin rings to use with my 20" rolling pin. Question is: 3 different rings came in the pack, which one so i use to roll out my fondant to cover cakes?
Mine came with a sheet telling me the thickness of each color. I usually roll with the 1/4" (I think they're yellow) rings until I get it spread out and even. I like my fondant thinner than that, but not quite as thin as 1/8" (the next ring size down) So, once it's an even 1/4" I take the rings off and just go over it all to make it a little thinner. You get a feel for the right thinness that works for you after a while.
That kind of depends on how thick you want the fondant on your cake to be - it varies. Try rolling out a little fondant with each pair of rings and see which one you like best. I personally like to cover cakes with fondant that's about 1/4-3/8" thick, because I find it easier to work with and it doesn't tear as often, but others like a thinner layer.