15/0 Miyuki Seedbeads
Tiny - 1 mm seedbeads - excellent for very fine embellishment. Also enjoyed by those who have been working with seedbeads for a while and are looking for the challenge of using smaller beads. Kind of like doing harder and harder Crosswords and Sudokus.
Many of the patterns in Laura McCabe's book on using Rivolis and other crystal components call for size 15/0s.
Miyuki 15/0 seed beads are round: approx 1.5mm OD with a 0.7mm hole, approximately 250/gram