Definition
A raised, thickened, or reinforced section of a casting, forging, or machined part, usually cylindrical, that provides extra material around a hole, shaft, or mounting point to add strength, support a bearing, or allow for threading.
Plain English
A small raised lump or pad built into a metal part to give it extra thickness where strength is needed — usually around a hole, a bolt point, or where a shaft passes through.
Context Anchor
Seen in aircraft engine and maintenance manuals when describing castings, housings, brackets, and other parts with reinforced attachment areas.
Derivation
From Old French 'boce' meaning a bump, swelling, or protuberance. The mechanical use kept the original sense — a deliberate bump of extra material on an otherwise flat or smooth surface.
Why Pilots Care
If a boss is cracked, worn, or damaged, the part attached there may not be properly supported or aligned, which can make the component unsafe to use.
Intuition Check
Boss does not mean a person in charge here. In maintenance, it means a raised or thickened area on a physical part.
Example Sentence 1
The technician inspected the boss around the bearing housing for cracks before reinstalling the shaft.
Example Sentence 2
Oil lines were secured to the threaded boss on the crankcase.