sew-classic recommends just the class 15 plastic bobbins these days because of the holes
I bought some metal class 15 from WM or somewhere and they were very light weight and flimsy.
I've had a few bobbins fall apart - use them to make crafts - earrings anybody?
When I find old bobbins, I remove the thread and if they are rusty I soak them in something to remove the rust then I brush them up and they are ok again most of the time - if not ok they get thrown away. I have seen a few old bent bobbins that really don't work and should be thrown away.