Not all Coins are the same Size
Coin Ring Sizes
I can craft a ring to fit sizes 1 through 18, but that does not explain how the ring will look or feel at said size. Coin sizes can vary from the small 21mm diameter Gold Swiss Franc to the massive 40.6mm diameter Silver American Eagle. Even the thickness of the coin can vary greatly too. The 90th Birthday Queen Elizabeth is am absolutely beautiful ring, but some ladies would be turned off by the thickness of the ring while others might like having such a think ring. It comes down to personal preference. Beauty and satifaction is in the eye of the wearer.
I really like the Silver Angel, but when I made it a size 12 to fit my finger I quickly realizes it was a massive coin ring. I personally did not believe the 'mass' of the coin on my hand looked good even though the ring itself looks amazing. Some people are the opposite, some like huge rings on their fingers. There is nothing wrong with that.
Where you run into a problem is when a person orders a Morgan size 6 thinking it will look nice on their small finger and it ends up being massive. The ring can be made to fit a size 6 finger, but making it a size 6 won't take away from the overall mass.
The flip side of this issue is if someone loves the look of the Gold Swiss Franc 20 and wants a size 12. The coin itself is not very big at 21mm and would undergo massive stretching to get it to size 12. Once you placed it on your finger, it would not be aetheticlly balanced on that finger.
Different coins tend to have ideal size ranges with some latitude. It would not be practically for me to list the size range of every coin ring here. I will share some pictures of various comparisons though to give you some idea that the mass of the coin can change drasticly from coin to coin. If your curious about a specific coin ring, you can email me and we can discus what would be your best options.
US Half Dollar
This is not a rule and latitude can be applied, but generally speaking the following chart will give you an idea for a starting point and their size ranges. As the ring is condensed, it will appear thicker. As the ring is stretched, it will appear thinner. How much it appears condensed or stretched will depend on the size of the coin and the desired fitted size.
Coin Ring Shape
I shape bands on a coin ring two different ways.
There is a curled band which has a slight curve to the shape of the band that is very similar to a traditional wedding band shape. The curve can be adjusted from a slight curve to more extreme curve depending on personal preference.
The other type of band shape is a straight band. It is what it sounds like, the outside band is straight. Please be aware that the inside band is not straight and has a slight taper. This happens because the inside (where the hole is punched) is normally thinner then the outside reed of the coin. Plus the inside section is stretched more during the coin ring making process.