They are found on every new ball pens and refills in India. I don't know the exact purpose of their existence, but I guess it has to do with leakage of ink.

I never thought I would see this question here! I now write with FPs exclusively, but removing those beads from newly bought pens were special experience to us as little kids! We fondly associated them with the joy of new pens. We used to call them "pearls".