Superduo Beads are a two holed Czech glass bead. Superduos are made to a more precise standard than regular Czech seeds. They measure 2.5x5mm, with two .8mm holes. They are not simply "coated crystal" but actual colored glass with a variety of coatings. They are packaged in 16 gram units. Each gram contains 15-17 beads depending on the coating of the bead.