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In engineering and construction, a nail is a pin-shaped, sharp object of hard metal, typically steel, used to fasten things together. It is driven into the workpiece by a hammer. Sometimes a nail holds materials together by friction alone; in other cases the point of the nail may be bent over or clinched to prevent it from pulling out. Nails are made in a great variety of forms for specialized purposes; the common everyday kind of nail is sometimes called a "wire nail" to distinguish it from nails in general. Some kinds of nails are referred to by other words, for example " pins", " tacks" or "brads".
Manufactured cut nails were first introduced in the United States in the late 1700s. Before that time, nails were hand-forged. Cut nails are machine-cut from flat sheets of steel. They are also called square nails because of their square appearance. Though still manufactured for historical renovations, cut nails have largely been replaced by mass-produced wire nails.
Types of nail include:
Nails are usually sold by weight (either in bulk or in boxes). In the United States of America, the length of a nail is designated by its penny size. It is believed that the origin of the term "penny" in relation to nail size is based on the old custom in England of selling nails by the hundred. A hundred nails that sold for sixpence were "six penny" nails. The larger the nail, the more a hundred nails would cost. Thus the larger nails have a larger number for its penny size. The penny size is written with a number and the abbreviation d for penny (e.g. - 10d). D is an abbreviation for denarius, a Roman coin similar to a penny; this was the abbreviation for a penny in the UK before decimalisation. A smaller number indicates a shorter nail and a larger number indicates a longer nail. Nails under 1-1/4 in., often called brads, are sold mostly in small packages with only a length designation (e.g. 1/2" (12 mm), 1-1/8" (28 mm), etc.).
In other English-speaking countries and the rest of the world, including Canada, nails are designated by type and length (not by penny) in rounded millimetres. For example, a nail with a size designation written as "50 x 3,0" would have a meaning of 50 mm in length and 3 mm in diameter.