Last week I needed six rings for a chandelier project. I made them by tacking a 5/16” round rod to a 1.25” round mandrel then wrapped a coil with torch heat until I had 8 or 9 rings. I generally make a few extra in case I misplace one or one doesn’t look just right. The extras are handy to weld on things as hangers.
I removed the rings from the mandrel by slicing the coil with a zip disc and opening each ring with a tweaker until it slipped off.
Sometimes it is important that a ring not be able to rotate so an ellipse is preferable. I have made several mandrels with crank shafts like a windlass to make chain links of different sizes. The principle is the same as the round rings, torch heat, wrap, sever and release.