Irregular four-sided black beads

These vintage Czechoslovakian glass beads were made during the 1980s or early 1990s. They were made in molds, but there are no mold marks. They are opaque shiny black. Each bead has four sides, but the sides are irregualr. The bead is 12 mm from hole to hole and the hole will accommodate up to a 0.5 mm cord. The bead is 8 mm wide. Price is for 10 beads.