Step 1: Cut some strips
Step 2: Make them round(ish)
Step 3: Weld (or maybe burn) the ends together
For the rings I overlap the ends by about a third of an inch, clamp both edges, welded the center, remove one vise grip, weld, repeat on the other edge. I only managed to burn a hole in one or two of them :-)
A quick cleanup job on a sander and they're ready to go.
After making these five I made another batch of nine 3.5" rings.