A ball-peen hammer has two ends — one ball-shaped and the other more cylindrical. It may have a metal, fiberglass or wooden handle. A ball-peen hammer is a variety of peening hammer used for both shaping and striking metal, including striking punches and chisels, in metal fabrication.
The ball-peen hammer's crowned, or rounded, edge works metal smoothly without marking it. The ball portion can straighten, soften and expand metal into the desired shape. The other, straighter end of the hammer can be used to strike punches and chisels. A chisel is a steel metal cutter that cuts sheet metal, rivets, bolts and even plaster. Punches mark metal or wood for placement of holes and a ball-peen hammer is used to strike the punch when an automatic punch is not used.
Actual peening is not used in most metal fabrication operations today, but it was the original use of peen hammers. Peening is striking welded or riveted metal to make it as flexible as the rest of the metal in an object. The result of peening is a strain-hardening property added to the metal.
Peening hammers include the cross peen and the straight peen as well as the ball-peen hammer. The straight peen hammer has a wedge-shaped rather than a ball-shaped head. The head is straight in a straight-peen hammer, while the cross peen hammer features the wedge-shaped head at a sideways angle. Peen hammers, spelled pein or pien in the United Kingdom (UK), have a steel head that has been hardened to prevent chipping during striking.
Peen hammers are also called engineer's hammers or machinist's hammers and come in many different weights, often from 2 ounces (56.7 g) to 48 ounces (1.3608 kg). This hammer can be used to form the overall shape of the metal object and can be used in making knife blades and swords. The newly-formed metal blade can first be roughly filed before being properly shaped with a ball-peen hammer.