Alan Hsu,
More than you ever wanted to know abt split rings: http://www.worthco.com/rings/spltring.html
***** is, you have to buy them 1K at a time!
(Check the parent for the "Key ring" family.)
Here is some info. that might help some.
The Sandwich Shoppe has small split rings & I read that
Cabela's sells them for fishing lures. After reading about
them being used on lures I just took some off old lures.
I hope this helps.