Nail (fastener)

In woodworking and construction, a 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.
History.
The history of the nail is divided roughly into three distinct periods: 
Hand wrought.
The first nails were made of wrought iron. Nails date back at least to Ancient Egypt—bronze nails found in Egypt have been dated 3400 BC. The Bible provides a number of references to nails, including the story in Judges of Jael the wife of Heber, who drives a nail (or tent-peg) into the temple of a sleeping Canaanite commander; the provision of iron for nails by King David for what would become Solomon's Temple; and in connection with the crucifixion of Christ.
The Romans made extensive use of nails. The Roman army, for example, left behind seven tons of nails when it evacuated the fortress of Inchtuthil in Perthshire in the United Kingdom in 86 to 87 CE.
The term "penny", as it refers to nails, probably originated in medieval England to describe the price of a hundred nails. Nails themselves were sufficiently valuable and standardized to be used as an informal medium of exchange.
Until around 1800 artisans known as "nailers" or "nailors" made nails by hand – note the surname Naylor.
At the time of the American Revolution, England was the largest manufacturer of nails in the world. Nails were expensive and difficult to obtain in the American colonies, so that abandoned houses were sometimes deliberately burned down to allow recovery of used nails from the ashes. This became such a problem in Virginia that a law was created to stop people from burning their houses when they moved. Families often had small nail-manufacturing setups in their homes; during bad weather and at night, the entire family might work at making nails for their own use and for barter. Thomas Jefferson wrote in a letter: "In our private pursuits it is a great advantage that every honest employment is deemed honorable. I am myself a nail maker." The growth of the trade in the American colonies was theoretically held back by the prohibition of new slitting mills in America by the Iron Act of 1750, though there is no evidence that the Act was actually enforced.
The production of wrought-iron nails continued well into the 19th century, but ultimately was reduced to nails for purposes for which the softer cut nails were unsuitable, including horseshoe nails.
Cut.
The slitting mill, introduced to England in 1590, simplified the production of nail rods, but the real first efforts to mechanise the nail-making process itself occurred between 1790 and 1820, initially in the United States and England, when various machines were invented to automate and speed up the process of making nails from bars of wrought iron. Also in Sweden in the early 1700s Christopher Polhem produced a nail cutting machine as part of his automated factory. These nails were known as "cut nails" or "square nails" because of their roughly rectangular cross section. Cut nails were one of the important factors in the increase in balloon framing beginning in the 1830s and thus the decline of timber framing with wooden joints. 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".
The cut-nail process was patented in America by Jacob Perkins in 1795 and in England by Joseph Dyer, who set up machinery in Birmingham. The process was designed to cut nails from sheets of iron, while making sure that the fibres of the iron ran down the nails. The Birmingham industry expanded in the following decades, and reached its greatest extent in the 1860s, after which it declined due to competition from wire nails, but continued until the outbreak of World War I.
Wire.
Wire nails are formed from wire. Usually coils of wire are drawn through a series of dies to reach a specific diameter, then cut into short rods that are then formed into nails. The nail tip is usually cut by a blade; the head is formed by reshaping the other end of the rod under high pressure. Other dies are used to cut grooves and ridges. Wire nails were also known as "French nails" for their country of origin. Belgian wire nails began to compete in England in 1863. Joseph Henry Nettlefold was making wire nails at Smethwick by 1875. Over the following decades, the nail-making process was almost completely automated. Eventually the industry had machines capable of quickly producing huge numbers of inexpensive nails with little or no human intervention.
With the introduction of cheap wire nails, the use of wrought iron for nail making quickly declined, as more slowly did the production of cut nails. In the United States, in 1892 more steel-wire nails were produced than cut nails. In 1913, 90% of manufactured nails were wire nails. Nails went from being rare and precious to being a cheap mass-produced commodity. Today almost all nails are manufactured from wire, but the term "wire nail" has come to refer to smaller nails, often available in a wider, more precise range of gauges than is typical for larger common and finish nails.
Materials.
Nails were formerly made of bronze or wrought iron and were crafted by blacksmiths and nailors. These crafts people used a heated square iron rod that they forged before they hammered the sides which formed a point. After reheating and cutting off, the blacksmith or nailor inserted the hot nail into an opening and hammered it. Later new ways of making nails was created using machines to sheer the nails before wiggling the bar sideways to produce a shank. For example, the Type A cut nails were sheared from an iron bar type guillotine using early machinery. This method was slightly altered until the 1820s when new heads on the nails' ends were pounded via a separate mechanical nail heading machine. In the 1810s, iron bars were flipped over after each stroke while the cutter set was at an angle. Every nail was then sheared off of taper allowing for an automatic grip of each nail which also formed their heads. Type B nails were created this way. In 1886, 10 percent of the nails that were made in the United States were of the soft steel wire variety and by 1892, steel wire nails overtook iron cut nails as the main type of nails that were being produced. In 1913, wire nails were 90 percent of all nails that were produced.
Today's nails are typically made of steel, often dipped or coated to prevent corrosion in harsh conditions or to improve adhesion. Ordinary nails for wood are usually of a soft, low-carbon or "mild" steel (about 0.1% carbon, the rest iron and perhaps a trace of silicon or manganese). Nails for concrete are harder, with 0.5–0.75% carbon.
Usage.
Types of nail include:
Sizes.
Most countries, except the United States, use a metric system for describing nail sizes. A "50 × 3.0" indicates a nail 50 mm long (not including the head) and 3 mm in diameter. Lengths are rounded to the nearest millimetre.
For example, finishing nail* sizes typically available from German suppliers are:
United States penny sizes.
In the United States, the length of a nail is designated by its penny size.
In art and religion.
Nails have been used in art, such as the Nail Men—a form of fundraising common in Germany and Austria during World War I.
Before the 1850s bocce and pétanque boules were wooden balls, sometimes partially reinforced with hand-forged nails. When cheap, plentiful machine-made nails became available, manufacturers began to produce the "boule cloutée"—a wooden core studded with nails to create an all-metal surface. Nails of different metals and colors (steel, brass, and copper) were used to create a wide variety of designs and patterns. Some of the old "boules cloutées" are genuine works of art and valued collector's items.
Once nails became cheap and widely available, they were often used in folk art and outsider art as a method of decorating a surface with metallic studs. Another common artistic use is the construction of sculpture from welded or brazed nails.
Nails were sometimes inscribed with incantations or signs intended for religious or mystical benefit, used at shrines or on the doors of houses for protection.