4. Peen

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If you have ever wondered where they came up with the name “ball peen hammer” for that particular tool (who hasn’t?), you’ll be pleased to know that the rounded end of the hammer is called the peen. You know, the one that looks pretty much useless for anything except hitting someone over the head with. “I can’t help thinking of Harold’s bald head whenever I see the shiny dome of the peen on my trusty hammer.”