Re: Bead Sizing
there are variances, especially if the beads are not made specifically for fly tying. Most of the metal beads made for tying have a counter sunk hole on the back side, which is good for two purposes- getting them around the hook bend and as a pocket to "hide" the head of the fly.
And while the charts above give a range of sizes, you will find the geometry of the hook design/s greatly influences your ability to place a bead on them. Your best bet is select the styles/sizes of hooks YOU want to use beads with, buy a small volume from any one vendor, fit them to the hooks, then buy a selection of colors and volumes that you think will serve your purposes for the near term.
Box them and put a note on the back of the box indicating which beads work with which hooks and sizes and who you bought them from... and HOPE that the next time you want to buy more, they are using the same supplier =)
Being a "TotAV" (Tyer of the Anal Variety) I went as far as to mount beads onto the hooks and place them in an independent box all ready for use. I have enough to tie about 100 each in a variety of sizes in 3 styles- a long curved shank, a short curved shank, and a standard length straight shank.