For most materials, we suggest that you submerge the item in a small amount of water and work alternately from both sides of the bead. Submerging the item in a bit of water helps prevent noxious dust. (Drilling/cutting most shell, for example, creates dust that is harmful for your lungs.)
By working from both ends of the bead, you can enlarge the hole to the size you want, keeping in mind that it will be slightly smaller at the midpoint, than it will be at the outside edges of the hole.
See Related Products tab for products and projects that go with this item.