The perfect bead for tying midges like the Pearl Jam, Periwinkle and any other small flies that require a small bead. Pat Dorsey's Mercury series are tied with an x-small clear glass bead. This includes the mercury baetis, mercury pheasant tail, mercury black beauty, mercury midge, and the mercury blood midge among many others. The other colors are great for creating small midges and nymphs - get creative!
Hook sizes for x-small glass beads: #20-#24
Just fished the Mercury Blood Midge I tied the other day on the Metolius River. It knocked them dead in the unusually cloudy water. I must say the x-small bead is a booger to get on the hook!!
So far the beads have met my expectations. But I have only had a chance to tie 6 flys with them.