3D printed Ring Jaws.

9mm thickness with a:
7mm depth stop
5mm depth stop
3mm depth stop

A 8mm ring will sit 1mm proud of the face of a 7mm depth jaw stop
A 6mm ring will sit 1mm proud of the face of a 5mm depth jaw stop
A 4mm ring will sit 1mm proud of the face of a 3mm depth jaw stop

Compatible Chucks:
Nova
Wen
SC3
Oneway
<mileage may vary>
Confirmed compatible.
WEN 4-inch 4-Jaw Model LA4444 Chuck

Might be compatible with other chucks and I will update as we find out.

Buyers note: These tools are quite durable but due to the fact that they are 3D printed you should take care in their use.  Routinely inspect them for damage and cease use or replace them if you observe any layer separation. 
Use them at your own risk and, as always, wear protective equipment.

*I do not recommend that these be left anywhere or used in ways that can reach high temperatures,

Example:  Drilling coins can get far too hot and melt them.