Normally the gemstone beads size is with the unit "mm", such as 6mm, 8mm 10mm. As the beads are made of natural stone rough, so the beads size is not a certain size such as 6.0mm or 8.0mm. Normally if we said it's 8mm, the beads size on a strand will be in size range of 7.9mm~ 8.5mm. Some maybe 8.0mm, some maybe 8.3mm or 8.4mm. Actually, 8.5mm beads are no big difference from 8.0mm when look by eye.