Definition
A hand-held striking tool with a steel head that has a flat face on one end for general hammering and a rounded (hemispherical) face, called the peen, on the other end. The peen is used for shaping metal, setting rivets, and rounding over the edges of pins and fasteners.
Plain English
A metalworker's hammer with one flat side and one rounded side. The rounded side is used to shape, spread, or smooth metal.
Context Anchor
Seen in aircraft maintenance tool lists, sheet-metal work, and shop procedures involving controlled work on metal parts.
Derivation
The word 'peen' comes from an old Scandinavian word meaning to beat or hammer thin. The 'ball peen' is simply the ball-shaped end used for that beating work, distinguishing it from other peen shapes like cross or straight peens.
Why Pilots Care
Mechanics rely on it for precise riveting and metal work that keeps airframe surfaces smooth and structurally sound.
Intuition Check
A ball peen hammer is not a general-purpose “hit anything” tool. The rounded end is for controlled metal work, and it should only be used where that kind of tool is appropriate.
Example Sentence 1
The mechanic used a ball peen hammer to gently set the solid rivets along the wing skin.
Example Sentence 2
During the repair, the mechanic reached for the ball peen hammer to shape the small dent out of the aluminum panel.