The hammers inside pianos are at Hammer (piano)
A claw hammer

A hammer is a tool for putting nails into objects such as wood. It has a long handle, and a tip with a flat end for hitting nails. The most common type of hammer (sometimes called a claw hammer) has a curved end (on the other side of the hitting end) for pulling nails out.

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Swinging a sledgehammer

A sledgehammer is a hammer that has a longer shaft, and a more massive head. The user can swing it with two hands and apply more force.

Hammers as weapons

Big hammers were sometimes used as weapons. A tiny hammer is also used inside most small arms.