Now you can make a matching set.
Step 1: Mark the Center
Center the coin in the carpenters square. Using a razor blade score a line in the center. Rotate the coin 90 degrees and score another line. Where the lines cross is the center. Now use a punch to mark the center. This helps you in the next step
Step 2: Clamp and Drill
Clamp the ring. Drill through the premarked center. You can progressively drill a bigger hole until it will fit on the mandrel your using. Or, you can just use a 3/8 spade bit like did. I used a pry bar as the mandrel.
Step 3: Hammer
Place a large hammer on a flat surface to serve as an anvil. Next, place the coin over the mandrel. Using a small hammer, hammer the edge of the coin at a 45 degree angle.
As you hammer rotate the mandrel and apply slight pressure towards the anvil. The ring will form a cone shape. Continue to hammer until the cone forms a cylindrical ring.
Once you have the ring shape you can continue to hammer causing the ring to expand in diameter. This is where you check it against the finger measurement it's being made for.
Important. As yor move the ring up the mandrel, flip it around. This helps to make the cone a cylinder.
Step 4: Mount the Ring
Find a socket bit just barely smaller then the ring. If you can't find a socket that's just right you can use a smaller socket and use something to wedge between the ring and socket. I use parachord when I need to.
After you press the ring on the socket, use a nut and bolt and secure it through the female end. The protruding end of the bolt will be used for mounting in the drill press.
Place a smaller coin under the socket while you tap the ring on. This leaves an even spacing to true the edges up.
Mount the assembly in the drill press and spin it round. You will shape the bottom side first.
Step 5: Shape
With the assembly spinning in the drill press, use progressively finner sand paper to make the ring it's final shape. I start with 80 grit, then 400, then 2000.
Spray the 400 and 2000 grit sand paper with water. This prevents the sand paper from getting clogged with metal particles. Again, this gets HOT! And don't breath the metal dust.
Flip the ring as needed. Use polishing compound to buff it to a shine. Now that the outside is nice, time for the inside.
Be careful not to mar the ring. Use the wood clamp to remove the ring from the socket. Flip the ring over and press it back onto the socket. Make sure you use a soft work surface when you hammer the ring on and off. I used the clamp it self.
Step 6: Smooth the Inside
Take a larger size drill bit and tape a piece of 1000 grit sand paper to it. Roll the paper around the bit with the direction of spin for the drill press. Smooth the inside and any sharp edges.