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 is useful for many tasks, such as striking punches and chisels (usually performed with the flat face of the hammer). The peening face is useful for rounding off edges of metal pins and fasteners, such as rivets. The ball face of the hammer can also be used to make gaskets for mating surfaces. Here are some other uses of a ball peen hammer:

• Shaping metal by beating on it
• Spreading metal quickly and evenly
• Dishing out metal using a swage
• Spreading out rivets
• Creating a textured surface on sheet metals and blacksmithed items

Its worth noting that while ball peen hammers are not required for most blacksmithing projects, they are handy tools to have in your workshop.