Hmmm. For a first go round I suggest 18 gauge 3/16. It has a lot of give and fitting the rings in is really easy. After that feel free to try it with almost all ring sizes. Your test is that if 8 rings will fit on 1 ring then it will work. Like with my latest micro cube I had use 4 links of a larger size and modify the inner layers 2 and 4 to be single and not doubled because 8 links wouldn't fit into that size link.