Ball-Pein Hammer

"A ball-peen or ball pein hammer, also known as a machinist's hammer,[1] is a type of peening hammer used in metalworking. It has two heads, one flat and the other, called the peen, rounded. It is distinguished from a cross-peen hammer, diagonal-peen hammer, point-peen hammer, or chisel-peen hammer by having a hemispherical peen." (Wiki)