NAIL

in the anatomy of humans and other primates, horny plate that grows on the back of each finger and toe at its outer end. It corresponds to the claw, hoof, or talon of other vertebrates. The nail is a platelike, keratinous, translucent structure that consists of highly specialized epithelial cells. The nail grows from a deep groove in the dermis of the skin. All nail growth occurs at the nail's base, where the specialized cells that make up the nail's plate are produced; these cells are pushed forward as new cells form behind them. The nail plate is also attached to the underlying, richly vascularized nail bed, which supplies the plate with necessary nutrients. The cells at the front edge of the nail plate die and turn white as they lose contact with the nail bed. The whitish, crescent-moon-shaped part of the nail, known as the lunula, is also not attached to the underlying nail bed. The nail's chief function is to protect the terminal portions of the toes and fingers. On the fingers, the front edge of the nail assists in the manipulation of small objects, as well as in scratching. in construction and carpentry, a slender metal shaft that is pointed at one end and flattened at the other end and is used for fastening one or more objects to each other. Nails are most commonly used to fasten pieces of wood together, but they are also used with plastic, drywall, masonry, and concrete. Nails are usually made of steel but can also be made of stainless steel, iron, copper, aluminum, or bronze. The pointed end of a nail is called the point, the shaft is called the shank, and the flattened part is called the head. Different types of nails 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. A box nail is similar to a common nail but has a slimmer shank and is used on lighter pieces of wood and on boxes. A casing nail is similar to a finishing nail but has a slightly thicker shaft and a cone-shaped head. Nails smaller than one inch long are called wire nails if they have a head and brads if they have a very small head or none at all. Extremely thick nails are called spikes. Nails can be given specially worked shanks to give them greater holding power once they have been driven in; the ring nail has annular rings on its shaft, while the spiral shank nail has a groove running up it in a tight spiral, like that of a screw. Roofing nails have large, flat heads that can better hold down materials such as roofing felt and fibreboard. Certain other nails are specially hardened so that they can be driven into masonry or concrete, usually in the act of attaching wooden members to these materials. Nails are made by feeding a thick, continuous steel wire into a machine where the wire is gripped between two dies and is cut to the desired length. Sufficient metal to form the head is allowed to protrude from the dies at one end and is then flattened into a head by a blow from a mechanized hammer. The other end of the piece of wire is cut into a point, after which the nail is ejected from the machine and may be smoothed (to remove the rough edges), polished, or plated. Wire-nail presses can produce nails at speeds of up to 800 per minute.