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I tried making stainless steel gymnastics rings a couple of years ago.
A chap in Bombay took a solid 28 mm stainless rod and made a die to bend it into a circle. And weld the ends to make it a full circle.
I welded an eye nut onto the top of the ring to hook the rings onto a ceiling.
Terrific plan. But as the rod passed through the die and bending unit, it left a deep impression on the inside of the ring. Almost like the inside of the ring had been hammered deliberately.
That ruled out an even radius on the inside of the ring. If we made rings, it would neither be consistent nor even.
But the hammered surface has some advantages. The increased surface area actually improves grip. And the grip pinches less than the relatively steeper radius of normal rings.
So the imperfect process produced something interesting that works.