Definition
The rounded, wedge-shaped, or specially formed end of a hammer head opposite the flat striking face. The peen is used for shaping, bending, riveting, or stretching metal rather than for general striking.
Plain English
The non-flat end of a hammer head, shaped for working metal. Different peen shapes (ball, cross, straight) are used for different metalworking jobs.
Context Anchor
Seen in aircraft maintenance, especially sheet-metal work, rivet work, and some repair instructions.
Derivation
From Old Norse 'pîna,' meaning to hammer or beat thin. The word entered English to describe the working end of a hammer used to shape metal — which is exactly how it's still used today.
Why Pilots Care
Aircraft maintenance often involves peening — for example, peening over the end of a rivet to lock it in place, or shot peening a metal surface to increase its fatigue resistance. Knowing what 'peen' refers to helps when reading maintenance manuals or tool lists.
Intuition Check
Peen does not mean simply denting or beating on metal. It means controlled metalworking done for a specific repair, forming, or surface-strengthening purpose.
Example Sentence 1
The mechanic used the ball peen of the hammer to set the rivet head.
Example Sentence 2
After driving the rivet, he flipped the hammer to peen the metal surface smooth.