How do I measure a bead hole's diameter?

Question

Simple as that, is there a tool to buy to accurately measure how many millimeters a bead hole's diameter is?

Answer 1

I believe needles are sized by guage.  Try to find a needle that fits and if it doesn't say on the label what size it is, you could take it to the hardware store and ask to handle a vernier caliper and SHAZAM! you just happen to have a needle to try it out on.