A screw is any shaft with a corkscrew-shaped groove formed on its surface. Screws are used to fasten two objects together. A screwdriver is a tool for driving (turning) screws; screwdrivers have a tip that fits into the head of a screw.

Early Screws

Around the first century CE, screw-shaped tools became common, however, historians do not know who invented the first. Early screws were made from wood and were used in wine presses, olive oil presses, and for pressing clothes. Metal screws and nuts used to fasten two objects together first appeared in the fifteenth century.

In 1770, English instrument maker, Jesse Ramsden (1735–1800) invented the first satisfactory screw-cutting lathe, and went on to inspire other inventors. In 1797, Englishman Henry Maudslay (1771–1831) invented a large screw-cutting lathe that made it possible to mass-produce accurately sized screws. In 1798, American machinist David Wilkinson (1771–1652) also invented machinery for the mass production of threaded metal screws.

Robertson Screw

In 1908, square-drive screws were invented by Canadian P. L. Robertson (1879–1951), 28 years before Henry Phillips patented his Phillips head screws, which are also square-drive screws. The Robertson screw is considered the "first recess-drive type fastener practical for production usage." The design became a North American standard, as published in the "Industrial Fasteners Institute Book of Fastener Standards." A square-drive head on a screw is an improvement over the slot head because the screwdriver will not slip out of the screw's head during installation. The early 20th century Model T car made by the Ford Motor Company (one of Robertson's first customers) used over seven hundred Robertson screws.

Phillips Head Screw and Other Improvements

In the early 1930s, the Phillips head screw was invented by Oregon businessman Henry Phillips (1889–1958). Automobile manufacturers now used car assembly lines. They needed screws that could take greater torque and could provide tighter fastenings. The Phillips head screw was compatible with the automated screwdrivers used in an assembly line.

A hexagonal or hex screw head has a hexagonal hole turned by an Allen key. An Allen key (or Allen wrench) is a hexagonally shaped turning tool (wrench), was first produced by William G. Allen of the Allen Manufacturing Company in Connecticut; who patented it first debatable.

In 1744, the flat-bladed bit for the carpenter's brace was invented, the precursor to the first simple screwdriver. Handheld screwdrivers first appeared after 1800.

Types of Screws

Myriad types of screws have been invented to perform specific tasks.

A cap screw has a convex head, usually hexagonal, designed to be driven by a spanner or wrench.

has a convex head, usually hexagonal, designed to be driven by a spanner or wrench. The wood screw has a tapered shaft allowing it to penetrate the undrilled wood.

has a tapered shaft allowing it to penetrate the undrilled wood. The machine screw has a cylindrical shaft and fits into a nut or a tapped hole, a small bolt.

has a cylindrical shaft and fits into a nut or a tapped hole, a small bolt. The self-tapping screw has a cylindrical shaft and a sharp thread that cuts its own hole, often used in sheet metal or plastic.

has a cylindrical shaft and a sharp thread that cuts its own hole, often used in sheet metal or plastic. A drywall screw is a specialized self-tapping screw with a cylindrical shaft that has proved to have uses far beyond its original application.

is a specialized self-tapping screw with a cylindrical shaft that has proved to have uses far beyond its original application. The set screw has no head at all and is designed to be inserted flush with or below the surface of the work piece.

has no head at all and is designed to be inserted flush with or below the surface of the work piece. The double-ended screw is a wood-screw with two pointed ends and no head. It is used for making hidden joints between two pieces of wood.

Shapes of Screw Head

Pan head : disc with a chamfered outer edge

: disc with a chamfered outer edge Cheesehead : disc with a cylindrical outer edge

: disc with a cylindrical outer edge Countersunk : conical, with flat outer face and tapering inner face allowing it to sink into the material, very common for wood screws

: conical, with flat outer face and tapering inner face allowing it to sink into the material, very common for wood screws Button or dome head screw : flat inner face and hemispherical outer face

or : flat inner face and hemispherical outer face Mirror screw head: countersunk head with a tapped hole to receive a separate screw-in chrome-plated cover; used for attaching mirrors

Types of Screw Drive

A variety of tools exists to drive screws into the material to be fixed. The hand tools used to drive slot-headed and cross-headed screws are called screwdrivers. A power tool that does the same job is a power screwdriver. The hand-tool for driving cap screws and other types is called a spanner (U.K. usage) or wrench (U.S. usage).

Slot head screws are driven by a flat-bladed screwdriver .

driven by a . Cross-head or Phillips screws have an X-shaped slot and are driven by a cross-head screwdriver , designed originally in the 1930s for use with mechanical screwing machines, intentionally made so the driver will ride out, or cam out, under strain to prevent over-tightening.

, designed originally in the 1930s for use with mechanical screwing machines, intentionally made so the driver will ride out, or cam out, under strain to prevent over-tightening. The Pozidriv is an improved Phillips head screw, and it has its own screwdriver, similar to cross-head but with better resistance to slipping, or cam-out.

is an improved Phillips head screw, and it has its own screwdriver, similar to cross-head but with better resistance to slipping, or cam-out. Hexagonal or hex screw heads have a hexagonal hole and are driven by a hexagonal wrench , sometimes called an Allen key or a power tool with a hexagonal bit.

, sometimes called an Allen key or a power tool with a hexagonal bit. Robertson drive head screws have a square hole and are driven by a special power-tool bit or screwdriver (this is a low-cost version of the hex head for domestic use).

drive head screws have a square hole and are driven by a special power-tool bit or screwdriver (this is a low-cost version of the hex head for domestic use). Torx head screws have a splined socket and receive a driver with a splined shaft.

Tamper-proof Torx's drive sockets have a projection to prevent a standard Torx driver being inserted.

Tri-Wing screws were used by Nintendo on its Gameboys, and don't have a driver associated with them, which has discouraged even minor home repairs to the units.

Nuts

Nuts are square, round, or hexagonal metal blocks with a screw thread on the inside. Nuts help fasten objects together and are used with screws or bolts.

Sources and Further Information