2.5-3.5mm round. This lot is a mixture of nailheads. Most of them are flat on one side and faceted on the other. Some have lines in them. Some are a bit larger than others. This is a nice lot of smaller antique nailhead beads. They are from the early 1900's. What a find! Glass nailhead beads were used in the days of the flapper to embellish garments before sequins were developed.