In engineering, woodworking and construction, a nail is a pin-shaped, sharp object of hard metal, typically steel, used as a fastener. Nails for specialised purposes may also be made of stainless steel, brass or aluminium.

Nails are typically driven into the workpiece by a hammer or by a nail gun driven by compressed air or a small explosive charge. A nail holds materials together by friction in the vertical direction and shear strength in lateral directions. The point of the nail is also sometimes 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". Very long nails are known as "spikes".

History

Nails go back at least to the Roman period. Until the end of the 18th century, they were always made by hand, a nailer providing them with a head and point. Until the early 17th century there were workmen called slitters who cut up iron bars to a suitable size for nailers to work on, but in 1590 the slitting mill was introduced to England, providing a mechanical means of producing rods of uniform cross-section. In the 19th century, after the invention of machines to make "cut nails", some nails continued to be made by hand, but the handmade nail industry gradually declined and was largely extinct by the end of that century.

Manufactured cut nails were first introduced in America at the end of the 18th century. Cut nails are machine-cut from flat sheets of steel (originally iron). They are also called square nails because of their roughly rectangular cross section. Though still used for historical renovations, and for heavy-duty applications, such as attaching boards to masonry walls, cut nails are much less common today than wire nails.

Nail sizes

Most countries, except the USA and Canada, use a metric system for describing nail sizes. A "50 x 3.0" indicates a nail 50 mm long (not including the head) and 3 mm in diameter. Lengths are rounded to the nearest millimeter.

Canada uses a similar system except nail lengths are given in inches.

US penny sizes

Nails are usually sold by weight (either in bulk or in boxes). In the US, the length of a nail is designated by its penny size. It is commonly 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 six pence 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. This classification system was still used in England in the 18th century, but is obsolete there.

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 1¼ in., often called brads, are sold mostly in small packages with only a length designation (e.g. ½" (12 mm), 1¹â�„₈" (28 mm), etc.).

Nail terminology

• Box - a wire nail with a head; box nails are smaller in diameter than common nails
• Bright - normal surface finish; not recommended for weather exposure
• Casing - a wire nail with a slightly larger head than finish nails; often used for flooring
• CC - "cement coated"; nail coated with adhesive for greater holding power
• Common - a common construction wire nail with a head: common nails are larger in diameter than box nails
• Duplex - a common nail with a second head; allowing for easy extraction
• Finish - a wire nail that does not have a "head"; can be easily concealed
• Galvanized - treated for resistance to corrosion and/or weather exposure
• Head - round flat metal piece affixed to the top of the nail; for increased holding power
• Length - distance from the head to the point of a nail
• Point - sharpened end opposite the "head"; for greater ease in driving
• Shank - the body the length of the nail between the head and the point; may be smooth, or may have rings or spirals for greater holding power
• Spikes - large nails (usually over 4" - 100 mm) are called spikes