I bought a key ring here and it fits perfectly: http://www.keyring.com/6mm1564diametersmallsplitkeyring.aspx
It's really hard to get the ring in the hole. I used pliers to straighten one end out a bit, twisted the ring through the hole and bent the ring back into shape.
bcheNice find! I remember a trick via Pinterest about separating the rings on smaller and much tighter key rings. Use a staple remover tool; you know the thing that looks like it has 2 upper and 2 lower fangs. However on something this small, beware your fingertips.
bcheHi bche,
Hmmm, I also purchased this 6mm key ring from your link and just tried it.
The tip from TRexSr below about using a staple remover helped me to get the ring open enough to put it on.
But I needed pliers to put it all the way through and it did scratch the finish. The ring is quite strong.
Also, the ring ends are sharp and almost touch each other- seems you have to bend and make this ring bigger (open it up permanently) or it is too small to swing freely.
We're working on the key ring issue...I did try this one and it didn't work as well for me.
Thanks for sharing though!