RounTrio - Zinc Iris. The RounTrio bead is a PotomacBeads exclusive made out of high-quality pressed Czech glass. RounTrios feature a smooth, round shape and 3 holes. This unique 3-holed bead is highly versatile and offers a broader range of design options. With a wide array of colors and finishes to choose from, you’re sure to find the inspiration you need to get creative and have fun. RounTrio beads measure 6mm and have a .8mm hole size. They come in packs of 300.