To make holes in beads I use a metal rod called a mandrel. The diameter of the mandrel dictates the diameter of the hole in the bead. The size of the hole is always slightly bigger than the diameter of the mandrel because each mandrel needs to be dipped in a coating of bead release so that the hot glass does not permanently adhere to the mandrel. This coating is cleaned out of the bead after the beads has been removed from the mandrel.
I have mandrels in many different sizes from 1 mm to 22 mm. 1 mm is about 3/64" and 22 mm is 7/8" so you can see I can make a wide variety of beads and bead holes to suit all needs.
The most common sizes of mandrel in use by lampworkers are 1.6 mm - 1/16" , 2.4 mm - 3/32" and 5 mm - 3/16". 1.6 mm are great for earring beads, 2.4 mm accept a cotton cord or leather thong and 5 mm are just the right size for the European Bracelet Systems that so many love.