Definition
A bolt with a smooth, precision-ground cylindrical section (the shoulder) between the head and the threaded portion. The shoulder has a larger diameter than the threads and is designed to act as a bearing surface or pivot, allowing parts to rotate or slide on it without wear from the threads.
Plain English
A bolt that has a smooth, polished section between the head and the threads. That smooth section is sized precisely so other parts can turn or pivot on it, while only the threaded end screws into place.
Context Anchor
Seen in aircraft maintenance where a bolt is used not just to fasten parts together, but also to act as a small pivot, spacer, or guide for a moving part.
Derivation
The smooth, unthreaded portion is called the 'shoulder' because, like a human shoulder, it forms a stepped transition between two different sections — here, between the bolt head and the narrower threaded shank.
Why Pilots Care
Provides precise spacing and allows smooth pivoting motion while maintaining structural integrity in moving flight controls and gear.
Intuition Check
Shoulder does not mean the body part here. It means the smooth step or support section on the bolt, usually just below the head.
Example Sentence 1
The mechanic replaced the worn shoulder bolt at the aileron bellcrank pivot during the inspection.
Example Sentence 2
During the 100-hour inspection, all shoulder bolts in the nose-gear torque links were checked for wear.