Wow! So many replies! I forgot to tick the "notify me" box - sorry guys.
OK, Jo is a girl (my sister). The picture is of a necklace made of lots of these rings. I would say that they are about 1cm in diameter for the whole ring and the coiled metal that makes the ring is approximately 0.5-1mm. They are definitely not beads or things you buy from a haberdashery as the guy who made the necklace in the US told her it was an industrial type spare part (and had the cheek to be flogging them for £100!).
I think that the seal assister idea is most likely - thanks Tony.
Thanks again for all of your comments (or most of them
)
Have remembered to tick the "notify me" box this time!
Katie