The hook also plays an important part. The bend, wire size, and barb will keep you from using some beads. I find a round bend to allow more bead sizes. I also use the seed glass beads and some 3mm plastic round beads. Bead reamers help to enlarge the hole of the bead. These come in different size and you can even get a motorized reamer. You can even get some 15/0 seed beads for tiny midges. 11/0 seed beads will fit on some size 10 hooks. I have used beads in 6/0, 8/0, 11/0, 15,0 and 3mm and larger. When using larger beads though, you have to do allot of reaming to get them to fit on the hook, or use them on tube flies.