Screw
A helical threaded fastener and one of the six simple machines.
Tknbeez · CC BY-SA 3.0
A screw is a fastener with a helical ridge running along its exterior, designed to be tightened or loosened by applying a twisting force, or torque, to its head. Its primary function is to join objects together, and it comes in many variations suited to different materials. Screws can be inserted into pre-drilled holes in assembled parts, or they can cut their own threads as they are driven in.
At one end, the head features a slot or other shape that typically requires a tool to apply the twisting force. Common tools for driving screws include screwdrivers, spanners, wrenches, coins, and hex keys. The head is generally larger than the screw’s body, creating a bearing surface that prevents the screw from being driven deeper than its length; an exception is the set screw, also known as a grub screw. The cylindrical section from beneath the head to the tip is called the shank, which may be fully or partially threaded. The distance between threads is known as the pitch.
Most screws are tightened by turning them clockwise, a configuration called a right-hand thread. Left-hand threads are used in special cases, such as when a screw will experience counterclockwise torque that would loosen a right-hand screw. For this reason, the left-side pedal of a bicycle has a left-hand thread. The screw mechanism is recognized as one of the six classical simple machines defined by Renaissance scientists.
**History**
Before screws became common, fasteners relied on concepts like dowels, pins, wedging, mortise-and-tenon joints, dovetails, nails (sometimes with clenched ends), forge welding, and various bindings with cord made from leather or fiber, using many kinds of knots. The screw was one of the last simple machines to be invented. It first appeared in Mesopotamia during the Neo-Assyrian period (911–609 BC), and later emerged in Ancient Egypt and Ancient Greece, where it was described by the Greek mathematician Archytas of Tarentum (428–350 BC). By the 1st century BC, wooden screws were widely used throughout the Mediterranean in screw presses for extracting olive oil and pressing grape juice for winemaking. The earliest known documentation of the screwdriver appears in the medieval Housebook of Wolfegg Castle, a manuscript written between 1475 and 1490. However, screwdrivers likely did not become common until after 1800, once threaded fasteners had become mass-produced.
Metal screws used as fasteners were rare in Europe before the 15th century, if they were known at all. The metal screw did not become a common fastener until machine tools for mass production were developed toward the end of the 18th century. This development took off in the 1760s and 1770s along two separate paths that soon converged.
The first path was pioneered by brothers Job and William Wyatt of Staffordshire, UK, who patented a machine in 1760 that could be called an early and prescient screw machine. It used a leadscrew to guide the cutter for the desired pitch, and the slot was cut with a rotary file while the main spindle remained still. The Wyatt brothers did not have a wood-screw factory running until 1776. Their enterprise failed, but new owners soon made it profitable, and by the 1780s they were producing 16,000 screws a day with only 30 employees—a level of industrial productivity that was revolutionary at the time.
Meanwhile, English instrument-maker Jesse Ramsden (1735–1800) worked on the toolmaking and instrument-making side of screw-cutting, and in 1777 he invented the first satisfactory screw-cutting lathe. British engineer Henry Maudslay (1771–1831) became famous for popularizing such lathes with his screw-cutting lathes of 1797 and 1800, which combined a leadscrew, slide rest, and change-gear gear train in the right proportions for industrial machining. In a sense, he unified the paths of the Wyatts and Ramsden, doing for machine screws what had already been done for wood screws—making production much easier and spurring commodification. His firm remained a leader in machine tools for decades. A misquote by James Nasmyth spread the idea that Maudslay had invented the slide rest, but this was incorrect; however, his lathes helped popularize it.
These developments from the 1760–1800 era, with the Wyatts and Maudslay as key drivers, greatly increased the use of threaded fasteners. Standardization of thread forms began almost immediately but was not quickly completed; it has been an evolving process ever since. Further improvements to mass production of screws continued to push unit prices lower throughout the 19th century. Mass production thus began in two forms: that of wood screws (metal screws for fixing wood) in specialized, single-purpose, high-volume machine tools; and that of low-count, toolroom-style production of machine screws or bolts (with V-threads) allowing easy selection among various pitches.
In 1821, Hardman Philips built the first screw factory in the United States—on Moshannon Creek, near Philipsburg—for manufacturing blunt metal screws. An expert in screw manufacture, Thomas Lever, was brought from England to run the factory. The mill used steam and water power, with hardwood charcoal as fuel. The screws were made from wire prepared by "rolling and wire drawing apparatus" from iron produced at a nearby forge. The screw mill was not a commercial success; it eventually failed due to competition from the lower-cost, gimlet-pointed screw, and ceased operations in 1836.
The American development of the turret lathe in the 1840s and the automatic screw machines derived from it in the 1870s drastically reduced the unit cost of threaded fasteners by increasingly automating the process.
Lore & Background
The gimlet-pointed screw was patented by Thomas J. The American development of the turret lathe (1840s) and automatic screw machines (1870s) drastically reduced unit costs. L. In the early 1930s, American Henry F. Phillips popularized the Phillips-head screw.
Reader's Guide
The screw is significant as one of the last of the six classical simple machines to be invented, with origins in the Neo-Assyrian period. Its development from wooden screws in ancient presses to metal fasteners in the 18th century enabled the Industrial Revolution, particularly through precision screws used in micrometers and lathes. The mass production of screws, pioneered by the Wyatt brothers and Henry Maudslay, transformed manufacturing by drastically lowering unit costs and increasing availability. Standardization of threadforms began in the late 18th century and continued through the 1940s with the ISO metric screw thread and Unified Thread Standard. The screw's legacy includes its role in holding objects together across countless applications, from simple household items to complex machinery. The evolution of drive types—from simple slots and squares to Robertson and Phillips heads—reflects ongoing innovation to improve ease of use and manufacturing efficiency. The screw remains a fundamental component of modern technology, with its basic mechanism unchanged for millennia.
Did You Know?
- The first documentation of the screwdriver appears in earlier manuscripts, including the works of Leonardo da Vinci, predating the medieval Housebook of Wolfegg Castle.
- While some bicycle pedals use a left-hand thread on the left side to prevent loosening, many modern bicycles use right-hand threads on both pedals with a different mechanism.
Origins and the Attribution Debate
The question of who first conceived the water screw remains one of engineering history's most contested puzzles. Archimedes of Syracuse has long been credited as the inventor, yet the evidence is far from conclusive. The Greek scholar Posidonius claimed Archimedes devised the device during a visit to Egypt between 283 and 246 BC, possibly inspired by a water wheel he observed in operation. Other historians, however, contend that Archimedes merely encountered a technology already in Egyptian use. Canadian archaeologist John Peter Oleson sharpened this doubt, noting that no literary or archaeological trace of the screw exists before roughly 250 BC and questioning why the device became so tightly bound to Archimedes's name without clear explanation. Assyriologist Stephanie Dalley pushed the timeline even further back, citing an inscription of King Sennacherib alongside references in Strabo and Philo of Byzantium to argue that bronze screws irrigated the Hanging Gardens of Babylon. A BBC documentary even had a screw built from Sennacherib's description to test feasibility, while scholar Yaman Boluk countered that if Dalley was correct, the Assyrian screws would have featured an opening in the outer cylinder and blades detached from it—unlike the joined-blade design in the reconstruction.
Ancient Spread and Gradual Decline
Once established, the water screw spread remarkably across the ancient world. Moschion recorded its use as a bilge pump aboard the great ship built for Hiero II of Syracuse, while Posidonius noted water screws draining Spanish mines. Archaeological remains have surfaced in Egypt, Spain, France, and Italy, and literary texts place the device in Mesopotamia, Syria, and Spain as well. Diodorus described screws irrigating the Nile Delta to supply military camps and nearby cities, and Vitruvius detailed a wooden eight-blade screw in his architectural treatise written between 27 and 22 BC. The earliest surviving visual depiction is a fresco at the villa Casa di P. Cornelius Teges in Pompeii, painted before the city's destruction in 79 AD. Yet by the end of the third century, the screw had largely vanished from European use. Oleson's investigation of Fayum suggested that by the late first century BC or first century AD, records of the device had already thinned considerably, possibly because screws were uncommon or simply not subject to taxation. Historian Lynn White Jr. proposed that the technology persisted in Visigothic and Islamic Spain, and Oleson theorised that Arab conquerors may have reintroduced the screw to Europe following their eighth-century conquest of the Iberian Peninsula.
Renaissance Revival and East-Asian Diffusion
After centuries of relative obscurity in Europe, the Archimedes' screw re-emerged during the Renaissance. The first post-antiquity illustration appeared in the 1405 manuscript Bellifortis by German engineer Konrad Kyeser. Leonardo da Vinci and Agostino Ramelli both depicted the device in their theatre-of-machine catalogues, while Galileo Galilei explained its mechanical function in his work Mecchanice. The screw found a particularly powerful application in the Dutch Golden Age, where polder mills—windmills driving Archimedes' screws—drained low-lying land by moving large volumes of water across small head differences. The technology also crossed into East Asia: in 1612, Italian Jesuit Sabatino de Ursis and Chinese official Xu Guangqi published Hydraulic Methods of the Far West, describing the screw's agricultural uses and construction. Despite scholarly praise, adoption in China and Korea remained limited. Albert Koenig suggested that imperial scholars' preference for philosophy, the high cost of producing a screw, and the impracticality of Vitruvius's particular design all contributed to its marginal status in those regions.
Modern Pumping and Turbine Applications
In the modern era, the Archimedes' screw has found renewed relevance in both pumping and power generation. As a pump, it remains widely deployed in wastewater treatment plants and for dewatering low-lying regions, turning a helical surface inside a pipe to lift water from a lower body into channels or treatment systems. The device's dual nature was formally recognised in 1991, when a patent for the Archimedes screw turbine was filed, with testing conducted between 1993 and 1995. Run in reverse, the screw functions as a small hydroelectric generator suited to low-head sites that traditional turbines cannot efficiently exploit. These screw turbines operate across a broad range of flows—from 0.01 to 14.5 cubic metres per second—and heads from 0.1 to 10 metres, filling a gap in the hydroelectric market where moderate flow rates and low heads make conventional high-performance technologies impractical. This versatility has cemented the screw's role as a practical, low-impact solution for renewable energy in settings where larger turbines simply cannot compete.
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Frequently Asked Questions
What is a Screw in construction and engineering?
A screw is a fastener featuring an external helical thread that you tighten or loosen by applying rotational force to its head. It comes in countless shapes and sizes tailored to different materials and applications.
Why is the Screw classified as a simple machine?
Renaissance-era scientists identified the screw mechanism as one of the six classical simple machines because it converts rotational input into linear output. That mechanical advantage lets a small twisting force produce strong clamping pressure.
How does a screw actually hold objects together?
When torque is applied to the head, the helical threads bite into the surrounding material, translating your rotational motion into a pulling or pushing force. This direct engagement is why screws are the go-to fastener for joining components in construction and manufacturing.
What makes a screw different from other fasteners?
Unlike a smooth nail or a plain bolt, a screw's threaded exterior grips the material directly, often removing the need for a separate nut or washer. That self-tapping quality is what gives the screw such a wide range of uses across wood, metal, and plastic.
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