Czech Twins and Superduo's. Sold by the 11.5 gram 2 inch tubes. Superduos' and Twins look very much alike at first glance. They both have a puffy oval shape and two holes, and they're both 5mm long. However, they differ slightly in a few ways.
1. Shape. Superduos (SDs) are more precisely manufactured and are more even in size and shape than Twins. This means less culling, or removing and throwing away, unusable beads from your stash. However, with any pressed glass bead, you will always have "goof" beads.
2. Mass. SDs are plumper than Twins; in addition to being more evenly shaped, each bead contains more glass.
3. Price. In general, Superduos tend to be more expensive than the basic colors of Twins. And there are less Superduo's in a tube than Twins: Superduo's are average 15 per gram. Twins average about 20 per gram.
4. Colors. Superduos are available in slightly different colors and finishes than Twin beads. Currently, there is a few more of the traditional Czech designer finishes on SDs than on Twins -- such as iridescent's and two-tones. But there are lots of interesting Twin colors as well, including color-lined varieties and pearl finishes.