Been tossing it around in what passes for my brain.
It’s the knobs.
Since chainmail is so “floppy”, the knobs would be perfect to hold a section flat. An open ring of chain, slightly larger than a chosen hole, could be threaded between two rings to join them. Tension on the mail with one hand would allow the open ring, wedged against the hole, to stand “gap up” while the other hand would use a pliers to close the ring.
Could prolly be explained better, but it does make sense.
Reasonable, although it would make more sense if they were made out of steel or iron.
One thing mitigating in favor of these being more or less trivial (amulets) is that AFAIK there’s no surviving description of their production or use for any kind of purpose at all. :^)