I have an old clear glass necklace that I am restringing, and am very puzzled by the bead holes - I am hoping someone can explain.

The beads are clear faceted cubes and the bead holes look like they have been drilled from one side because the hole is very much larger on one side than the other, the hole is conical. They are glass not rock crystal. Hopefully two photos are attached.

I've never seen glass beads like this before - please can someone explain the why where and when

Thank you