I bought some vintage bottle caps from Ebay for another project. You can buy anything on Ebay. They came slightly flattened so that the fluted edges flared out. This was good when using them for jewelry as nothing dug into my neck. You can flatten your own bottle caps with a rubber mallet and a steel bench block.
I used my smallest hole punch to make a hole in the rim of the cap through which I threaded an eye pin. I spiraled the long end of the pin and glued it in place with Goop.
To add some weight to the cap, I covered the spiral with a penny.