This particular strand or Peridot has been hand polished in India.  Like most of ours stones that are polished in India, a 6mm round stone is 5.5mm.
The 4mm beads are 3.8-4mm .
Peridot Spiritual Energy

Peridot is a crystal of positive power, a talisman for recognizing and honoring the Creator’s frequency of Love, the source of all abundance. Used with right intent, it helps expand one’s ability to receive from the Universe on all levels of life.