A ball peen hammer, also known as a machinists hammer, is a type of peening hammer used in metalworking. It has two heads, one flat and the other, called the peen, rounded. The ball peen hammer was originally designed for peening, or shaping metal materials by hammering. One end of the head is ball-shaped for this purpose, while the other end is flat and is used for driving. Here are some common uses of a ball peen hammer:

• Peening: The ball peen hammer is useful for peening, which is surface hardening by impact. It is used to shape metal materials by hammering, such as rounding off edges of metal pins and fasteners, like rivets.

• Striking punches and chisels: The flat face of the hammer is useful for striking punches and chisels.

• Making gaskets: The ball face of the hammer can also be used to make gaskets for mating surfaces.

• General sheet metal work: The domed end of the ball peen hammer is useful for general sheet metal work sometimes as well.

• Dimpling holes in drywall: The round side of a ball peen hammer can be used to "dimple" small holes in drywall so that spackle/mud will be flush with the wall surface.

Ball peen hammers are commonly used in metalwork to drive punches and cold chisels, set rivets, and shape metal. They are also used by blacksmiths during the forging process to deliver blows for forging or to strike other forging tools.