Czech Glass Superduos are a type of 2-hole seed beads that are known for their unique shape and versatility in beadwork. They measure 5mm in length, 2.5mm in width, and 3.5mm in thickness, with two 0.8mm holes that allow for intricate designs. These beads are sold in hangable plastic tubes, with each tube containing approximately 22.5 grams or 320 beads.