Definition
A thickened, raised area of material around a bolt hole in a casting or structural part, designed to provide additional strength and bearing surface where a bolt passes through.
Plain English
An extra-thick spot built up around a bolt hole so the bolt has solid, strong material to clamp against and won't crush or crack the part.
Context Anchor
Seen in aircraft maintenance descriptions, especially around engine parts, brackets, housings, and other parts held together by bolts.
Derivation
Boss' in mechanical engineering comes from Old French 'boce', meaning a raised lump or protuberance. It describes any localized thickening on a part — here, the thickening is specifically built up around a bolt hole.
Why Pilots Care
Bolt bosses maintain structural integrity at attachment points subject to vibration, torque, and flight loads.
Analogy
A bolt boss is like the thickened area around a screw hole on a sturdy plastic cover. The extra material keeps the screw from crushing or tearing through the part.
Intuition Check
“Boss” does not mean a person in charge here. It means a raised, reinforced area of a part, usually built around a hole for a bolt.
Example Sentence 1
The mechanic inspected each bolt boss on the engine case for cracks before reassembly.
Example Sentence 2
Even torque applied to the bolts in the wing spar bolt bosses prevents distortion under load.