Three slightly different designs, one just the Graphene form, one with the Steem logo and one in the SonG theme. Free for you to download, to use, to mashup, to sell for money, whatever you like, as long as you keep true to free culture. Meaning Creative Commons BY SA license.
This could be done in plastic, I guess, but small details would be better visible in metal 3D prints. The design is pretty rough, the ring solid, it is 'there' like: WHAM! The 3D printing price of several materials even isn't that steep this time, except Gold. But that might speek for itself.
Graphene ring:
Download the Graphene ring STL file: CLICK HERE
Steem(It) ring
Download the Steem(it) ring STL file: CLICK HERE
SonG ring
Download SonG ring STL file: CLICK HERE
All my free 3d printable designs are availble in my BOX folder: CLICK HERE TO OPEN
The inner section is 21 mm, so just calculate to the wanted cross section and adjust the scale acordingly.