Nail is a small object made of metal (or wood, called a tree nail or “trunnel”) which is used as a fastener, as a peg to hang something, or sometimes as a decoration. Generally, nails have a sharp point on one end and a flattened head on the other, but headless nails are available. Nails are made in a great variety of forms for specialized purposes. The most common is a wire nail. Other types of nails include pins, tacks, brads, spikes, and cleats.
Nails are typically driven into the workpiece by a hammer or pneumatic nail gun. A nail holds materials together by friction in the axial direction and shear strength laterally. The point of the nail is also sometimes bent over or clinched after driving to prevent pulling out.
There are many different types of nails, the types depending on the material that they are driven into and the degree of holding power that they must have. Two basic classes of nails are common nails and finishing nails (see Figure). The most widely used of all nails, the common nail has a large, flat head that is driven in so that it is flush with the material’s surface. A finishing nail has a smaller, narrower head that is driven in below the material’s surface with a special tool called a nail set, or punch; the small depression remaining is filled in with putty. Because of their neater appearance, finishing nails are used mostly for interior paneling and cabinetwork.