Definition
A drill bit with a hollow center, used to cut a circular groove around a broken bolt or stud so the remaining shank can be removed without damaging the surrounding threads in the parent material.
Plain English
A drill that cuts a ring-shaped slot rather than a solid hole, leaving a small core of material in the middle. In maintenance, it is used to drill around a broken-off bolt so the broken piece can be lifted out without harming the threads in the part it was screwed into.
Context Anchor
Seen in aircraft maintenance and shop work when a round hole must be cut in sheet metal or another aircraft part.
Derivation
"Hollow" simply means empty in the middle. The name describes the bit itself: unlike a standard twist drill that removes all the material in its path, this one is empty in the center, so it cuts only a circular trench and leaves the core intact.
Why Pilots Care
Pilots rarely use a hollow drill themselves, but understanding the tool helps when reading maintenance records or discussing repairs with a mechanic. It explains how a broken bolt can be removed without scrapping an expensive component.
Analogy
Think of a cookie cutter pressed into dough: it cuts a clean ring and leaves the inner disc untouched. A hollow drill works the same way in metal.
Intuition Check
Do not read hollow as weak or incomplete here. It means the drill is open in the center and cuts around the edge of the hole.
Example Sentence 1
The mechanic used a hollow drill to remove the broken exhaust stud without damaging the threads in the cylinder.
Example Sentence 2
A hollow drill was used to create the oil passage in the propeller hub while keeping the surrounding metal intact.