This video shows how to make a full ring from parts in your libraries.  I will make another one soon to specifically show just the shanks.  For now here is a quick rundown of the process.

1.   start with your correct ring rail size.
2. pull out (import) the shank you want from your library.
3. 3D scale your shank to your finger rail size
4. use the outside shank selection set to easily select the outside of your shank
5. 2D scale your outside shank to the desired thickness. 
6. Do any other scaling or adjusting necessary such as widening the ring, adding to it or moving edges to adapt the shank to your project.  That's it.