My first thumb ring that I made.

I ordered a thumb ring when I ordered my bow, but getting the perfect fitment ring was hard, specially ordering it through online.
The fitment of thumb ring is very very important, and I must have found one.  Since I live in the states, and I did not know anybody who was into archery, specially Korean archery, I researched it online.
I found 2 very good online sources for Asian archery.
ATARNet
Korean Traditional archery 

I asked many questions on those forums, and got good information.

I bought a billiard ball from Amazon, and made my first thumb ring.

I made it without too much knowledge, and of course, it was failure.  After a few shots of arrows, my thumb was hurt.  I had to make another one.