A screw is one of the six classical simple machines (the others being the lever, wheel and axle, pulley, inclined plane, and wedge). It converts rotational motion into linear motion. It’s a simple machine, but it’s one of the most important we have. Screws are everywhere — in your furniture, in your dishwasher, in factories, and in rocket ships. They play an integral role in the simplest to the most complex machinery we have in the highly advanced technological world of today. But where did it all begin?
Early Greek Origins
If you ask the Greeks, a scientist by the name of Archytas of Tarentum — sometimes called the founder of modern mechanics — invented the screw circa 400 BC. However, the concept of a screw, known as the “screw principle,” was around long before Archytas. We have evidence that the screw principle was first applied in the form of the screw press, used in ancient Greece and Egypt to extract oil from olives and juice from grapes.
Famed mathematician Archimedes is also sometimes credited with inventing the screw. Around 234 BC he used the screw principle to construct what is now known in physics as “Archimedes’ screw” (also called a screw pump), which was used to pull water up from shallow irrigation ditches and extract bilge water from the hulls of ships. Archimedes was also the first scientist to study the screw as a machine, giving further weight to his claim as the inventor of the screw.
In 52 AD, Heron of Alexandria, another Greek mathematician and engineer, identified the screw as a classical machine, one of the five mechanisms that could “set a load in motion.” Italian physicist and engineer Galileo Galilei was the first to produce a complete dynamic theory of simple machines — including the screw — which he published in 1600 in Le Meccaniche (“On Mechanics”).
The Key to Modern Industry
Though useful, screws were laborious to make during ancient times. Screw threads (the raised ridges that circle the core cylinder) had to be cut by hand by skilled craftsmen. Screws thus gained limited application in ancient times. It wasn’t until screw-cutting lathes were invented in the 15th century that screws began to be used as fasteners, augers, and drills. Screw fasteners were first used to build clocks, and we see our first evidence of screws applied to drilling when augers and drills started appearing in European paintings around this time.
In 1750, a clockmaker named Antoine Thiout developed the first lathe equipped with a screw drive. This innovation allowed the tool to be moved semi automatically. However, his design was still rudimentary. It wasn’t until 1770 that another engineer, Jesse Ramsden, improved upon the design. He created what is known as the first “satisfactory” screw-cutting lathe, capable of cutting precision screws. Precision screws could be used to build precision instruments, such as steam engines and assembly lines. From there, screw innovation really took off — it’s no coincidence that the Industrial Revolution reached full steam around this same time.
Soon enough, screws themselves were being factory-made. But not until one more obstacle was overcome. Although the screw-cutting lathe greatly enhanced production, there was still the problem of standardization. Everyone who was producing screws was producing them to their own specifications.
An English engineer named Joseph Whitworth took it upon himself to solve the problem. He collected sample screws from dozens of factories across England, surveying threads and widths. Analyzing his data, he submitted two proposals in 1841:
- Screw thread flanks should be a standard 55 degrees.
- The number of threads per inch (thread pitch) should also be standardized for various screw diameters.
By the 1860s, his proposals were standard practice in England. Independently of Joseph Whitworth, in 1864 an American engineer named William Sellers proposed a different set of screw standards based on a 60-degree thread flank, with thread pitches also standardized according to diameter. Sellers’ proposal became the U.S. Standard.
The Future of Screws
It’s not an understatement to say that screws hold society together. Without them, everything in your home, your office, and on the road would fall apart. But the screw’s work isn’t done. As long as new technology is being developed and old technology being improved, there will be cause to design new threaded screws to rise to the occasion.