I've been using glass beads for everything from chronomids to salt bait fish patterns they are fun to tie with and work well too. Depending on the fly I've used 4/0, 6/0, 8/0, 10/0, 11/0, and 15/0, in many colors and finnishes. They do break up if you keep pounding them on the rocks with your backcast. Depending on how you tied them you can replace the beads easily. There are so many colors and patterns to use. The challenge is endless , try Joe Warrens book for ideas. 'Tying Glass Bead Flies', pub by Amato Books.