What small inventions can be made with a thin steel pipe?

1. Americans invented the pen in the modern sense. In the Middle Ages, people wrote with sharpened goose feathers, which was called quill pens. Before the fountain pen was invented, Europeans had used quill pens for thousands of years, also called quill pens. It is made of the wing feathers of chickens, ducks, geese, eagles and other birds, and the most commonly used one is goose wing feathers. The word "pen" in English comes from the Latin word "feather". However, the life of quill pens is very short, and the nib is easy to be bald or bifurcated. It is good that a pen can write thousands of words. Later, people wrapped a layer of metal foil on the tip of quill pens, and the metal tip was born. On September 23rd, 1809, mass-produced pens went on sale in Britain. From 65438 to 0884, Edersen wortmann, an American, applied the capillary principle to design a component with capillary function-the pen tongue, which was closely matched with the pen tip, and then used a dropper to inject ink into the hollow pen holder. By virtue of capillary attraction, ink automatically flows to the nib, forming the prototype of fountain pen. Wortmann's original pen had a primitive note system. The owner of the pen must use a dropper to inject ink into the straw of the pen. Since then, there have been more than 400 patents around pens. These improvements include: making elastic rubber pen container, using the principle of atmospheric pressure difference, designing water absorption structure to replace dropper for water injection. In addition, the pen holder and the pen container are also made, so that the fountain pen has the functions of protection and portability. At the beginning of the 20th century, pens with rubber tubes for squeezing and absorbing ink became popular. Since then, there has also been a fountain pen with a lever, which squeezes a rubber tube and automatically injects ink. Although there are many different types of pens commonly used now, many people prefer the smooth writing function of fountain pens.