I make all my own hollow silver cube beads. I get different sized
square tubing, cut them to the sizes I want, solder a silver square
disk at the open ends. I am careful to drill holes before soldering
for gases to escape I prefer to drill the holes through the square
tubing, as I can get them more perfectly centered. Sometimes I want
the holes in the center of the bead, or sometimes closer to the top
of the bead. Easy to do.