Well yes, they are universal as in it’s a ring going around your cock and balls and it’s using a standard measurement. Does that mean the exact same size will fit you? No, because designs vary.
What sizing with the CB-6000 rings will give you is a very good guide to what size you’ll want to wear, but if you’re moving to a solid metal ring like the one we recommend then that’s a rounded ring so a bit different (and way more comfortable I’m told).
The advice we followed was to use the inside diameter (obviously) of your CB-6000 plastic ring and get the size below when moving to a metal ring. So having looked it up, we used the 45mm CB-6000 ring, so hubby bought the 40mm base ring on the metal cage we use. But I think extra rings are only about £8 so if you’re not sure, just buy the one the same size and another one size smaller and you’ll have a good fit.
However, it’s not really about the ring size if you have small balls as you said, it’s the gap between cage and the ring, surely? So you just need to make sure that’s small. Hubby’s NEVER had a ball escape with the metal cage, with the plastic ones it happened occasionally as they bend a bit.
Definitely worth trying a metal cage before you get pierced, although any pierced cage is very secure by definition. I quite like the idea of it, but more as I’m thinking it might be hot to have him secretly pierced than the total security it would provide.