This item is not going to be carried by Gesswein, sizes available while they last. This tip of this hollow brass drill measures 3.10mm on the outside and 2.51mm on the inside.
Hollow brass drills used with Diamond Drilling Compound to make holes in stones without cracking them. Gently apply drill to surface on which diamond compound has been applied. Use slow speed and let up on drill frequently. Makes perfect holes in onyx, ruby, etc. Due to large shank size, use with #30 handpiece. Must be used with Lubricant/Thinner.