A ball-pein hammer is a type of hammer commonly used in metalworking. It has one flat and one hemispherical end. It is one of many useful hammers to have in the tool kit as it can be used for striking chisels and punches with the flat face of the hammer. The ball face is useful for rounding off edges of metal pins and fasteners, such as rivets so it does have its uses in woodworking too.
Spear & Jackson make good quality and affordable hammers with traditional hickory handles.