this will hold about 100 9.5mm steel balls. but some might fall if your running etc
but will hold about 33 and none fall.
they do different sizes/ amounts. i thought that this was enough for me. there are slightly thicker ones 5mm ,these are 3mm.and they sell in 20's that makes it cheaper and i think that 4 5mm thick would do.
you could pass the other 4 sets on.
these are so strong they're hard to separate and will nip you as they jump together.so beware. lol