A hammer is a tool meant to deliver blows to a target, causing it to move or deform. The most common uses are for driving nails, fitting parts, and breaking up objects. Hammers are often designed for a specific purpose, and so their design varies quite a lot. Usual features are a handle and a head, with most of the weight in the head. The basic design is hand-operated, but there are also many mechanically operated models for heavier uses. The hammer is a basic tool of many professions, and can also be used as weapon. Either way, it is perhaps the oldest human tool, perhaps even older than the earliest Homo species. By analogy, the name hammer has also been used for many mechanical parts and devices that are designed to deliver blows, e.g. in the caplock mechanism of firearms.