1. Picked up a piece of Titanium rod from eBay 1" diameter by 1 1/4 length. That is enough for three rings.
2. Determine the final diameter you need. I used 15/16 inch and turn the rod to that diameter.
3. Cut off enough for a ring. I used 8.5 mm.
4. Face both ends.
5. Hold the ring blank in a pair of pliers and hammer as desired with a ball peen hammer. You will need to pound it quite hard on an anvil or something solid.
6. Reface the ends of the blank.
7. Drill a center hole. I use several bit increasing in size to near the ring size desired.
8. Turn the inside of the ring to final ring size using a lathe.
9. Make slight bevels on the sharp edges to your liking.
10. Polish.
Use the same technique for a female version just adjust the outside diameter, width and ring size as necessary.