What old millstones were there in ancient China?

A person's eyes. According to relevant data, the old millstone bead in ancient Chinese is a metaphor, which refers to a person's eyes. In ancient times, the millstone was a grinding tool, which consisted of two circular stone disks with some stones or iron beads between them, which were used to grind grains into powder. The stone or iron ball sandwiched between grinding discs is round. The ancients used "beads" to describe eyes and "grindstones" to describe people's faces. The ancients often used this metaphor to describe a person's image or personality characteristics.