Why are all screws tightened clockwise?

The corresponding English word for a screw is Screw This word has undergone significant changes in meaning over the past few hundred years, at least until 1725, when it meant 'mating'.
In addition to the knowledge in its name, it took thousands of years for the small screw to be invented and regulated to be tightened clockwise and loosened counterclockwise.

Plato's friend invented the screw

The six simplest mechanical tools are: screws, inclined surfaces, levers, pulleys, wedges, wheels, and axles.
Screws are among the six simple machines, but to put it simply, they are just an axis and an inclined plane winding around it. Today, screws have developed standard sizes. The typical method of using screws is to tighten them with clockwise rotation (in contrast, loosen them with counterclockwise rotation).

Screws are not a long-standing invention. This tool, which we are accustomed to, took a whopping 2000 years to   invent, which serves as a powerful example of what it means to have high eyes but low hands.
People believe that Archiytas of Tarentum, a friend of Plato, invented screws in 400 BC. Archimedes was the first to realize that screws could be used to connect things together and also to lift water. The Romans used bronze and silver as materials and manually cut screws. In the early days, people used various types of screws to press olive oil, irrigate water channels, remove accumulated water from the bottom of cabins, and of course, to connect things together.

Clockwise tightening is mainly determined by the right-hand turn

However, due to the fact that the screws at the beginning of their invention were all handmade, the fineness of their screws was not consistent and was often determined by the personal preferences of the craftsmen.
In the mid-16th century, French court engineer Jaques Besson invented a lathe that could be cut into screws, and later this technology took 100 years to be promoted. Henry Maudsley, an Englishman, invented the modern lathe in 1797, which significantly improved the precision of threads. However, there is still no unified standard for the size and fineness of screws.

This situation changed in 1841. Maudsley's apprentice Joseph Whitworth submitted an article to the Society of Municipal Engineers calling for the integration of screw models. He made two suggestions: 1. The inclination angle of the screw thread should be based on 55 ° as the standard; 2. Regardless of the diameter of the screw, a certain standard should be adopted for the number of threads per foot.
It seems to be an unwritten rule that screws should be tightened clockwise, because right-handed people   use   their right hand to tighten screws clockwise with greater force, and most people are right-handed(about70%- 90%).

Although screws are small, they require n types of machine tools and n+1 types of cutting tools to be made in the early days

Anyway, Whitworth's ideas are very popular. Shortly after his proposal, the UK adopted the standard for round bottomed pointed screws, and in the 1860s, the United States and Canada also adopted this standard. However, screws are not easy to manufacture because their production process requires three types of cutting tools and two types of machine tools.
In order to solve the production and manufacturing problems of the British standard, American William Sellers invented a flat top and flat heel thread in 1864. This small change made it possible to manufacture screws with only one tool and machine tool. Faster, simpler, and cheaper. The thread of Sellers screws became popular in the United States and quickly became the application standard for American railway companies (two of which were busy building intercontinental railways).

The British insisted on using Whitworth's slightly picky screws, but these inconsistent standards still caused a lot of trouble during World War II. At that time, the armies of Britain, Canada, and the United States confused their equipment parts with maintenance parts. After the war, Canada, the United States, and the United Kingdom reached an agreement in 1949 to unify the thread standard - based on the British system, using a 60 degree inclination angle.
Later, Britain shifted towards a public system of measurement. In 1960, both the International System of Units and ISO metric standard screws in the country used threads with a 60 degree inclination angle. Looking at the world, clockwise rotating screws based on the metric system have become the standard. But in the United States, about 60% of threads still use inch based screw standards.