They use a special dril bit that is flexible and drill out the marrow center then it is drilled from the end where the lamp is back to the first pass, if messed up they use a 2 part epoxy to fix the hole and then paint to match. All the lamp makers wont let people in their shops to see it or there would be too much compitition. Ive tried finding out where I could get one of bits , but no luck so far.