Due to the fact that the Kazuri beads are hand-made, the holes can be somewhat inconsistent. They are supposed to be 2 mm - however, my experience has  been as follows. I've generally not had a problem with 16g round wire or higher. 14g wire probably works 80% of the time. 12g wire is doable, but may be problematic.

I also know that if you put the beads on cord, 2mm leather is generally too thick, but will work sometimes. I generally recommend 1.5mm leather.

If you are concerned about hole size, at the very end of the order process there is a comment box where you can send me a note letting me know what gauge size you are working with and I will make sure the beads you have chosen will fit.