Why are screws mostly tightened clockwise?

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The English word for screw is Screw. The meaning of this word has changed considerably over the past few hundred years; at least by 1725, it meant “to mate”. Beyond the scholarly significance of its name, the little screw has gone through thousands of years since its invention, during which it was established that it should be tightened clockwise and loosened counterclockwise. Why does a screw have to be tightened clockwise? Plato’s friend invented the screw. The six simplest mechanical tools are: the screw, the inclined plane, the lever, the pulley, the wedge, the wheel, and the axle. The screw is one of the six simple machines, but at its core it is nothing more than a shaft with an inclined plane winding around it. To this day, screws have developed standard sizes. The typical method of using a screw is to tighten it by turning clockwise (whereas it is loosened by turning counter-clockwise). Turning clockwise to tighten it is primarily determined by right-handedness. However, since the screws used in the early days of this invention were all hand-crafted, their precision varied, often depending on the individual preferences of the craftsmen. By the mid-16th century, French court engineer Jacques Besson invented a lathe that could be used to cut screws, and it took another 100 years for this technology to be widely adopted. The Britishman Henry Maudsley invented the modern lathe in 1797, and with it, the precision of threads was significantly improved. Nevertheless, 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 Institution of Civil Engineers calling for the standardization of screw sizes. He made two suggestions: 1. The inclination angle of the screw thread should be standardized at 55° ； 2. Regardless of the screw diameter, a certain standard should be adopted for the number of threads per foot. Although screws are small, in the early days they required n types of machine tools and n+1 types of cutting tools to be manufactured. Early screws were not easy to produce, as their manufacturing process \"required three types of cutting tools and two types of machine tools\". To address the manufacturing issues associated with the British standard, the American William Sellers invented a screw with a flat top and flat heel in 1864; this small change meant that only one type of cutting tool and machine was needed to manufacture screws. Faster, simpler, and cheaper. The threads of Sellers’ screws became popular in the United States, and soon became the standard for use by American railway companies. Properties of bolted connections – Main variables in the tightening process: (1) Torque (T): The tightening force applied, measured in Newton-meters (Nm) ； (2) Clamping force (F): The actual axial clamping (compressive) force between the connected components, measured in newtons (N) ； (3) Friction coefficient (U): The torque coefficient consumed in bolt heads, threaded pairs, etc ； (4) Angle of rotation (A): The angular distance that the thread must rotate under a certain torque, in order to cause the bolt to experience a certain amount of axial elongation or for the connection element to be compressed.