Paper clips seem to be the simplest of all inventions. It's just a short piece of curved metal wire for holding paper. But the paper clip was designed many times to make the shape we use today. People used to pin pages together. But the needle will damage the paper, and it will also stab the user's fingers. A Norwegian inventor named John E. Walker thought he could solve this problem. At 190 1, he filed a patent application for a wire paper clip. Almost at the same time, several inventors also proposed similar designs. Glanville paper clip is based on the traditional double-ring design, which has a part described by the manufacturer as "lips". The inner ring is slightly bent upward, which helps to push in smoothly. However, all these early paper clips have some problems. When the clip is pushed, the protruding end of the metal wire will pierce the paper, which may even damage the paper more easily than the needle. It is also difficult to make a machine for making clips. Obviously, the labor cost of producing paper clips by hand will make the product price too high. William Middlebrook, an engineer in Fort Worth, Connecticut, solved the problem of machine building. He invented a machine for bending wire paper clips in 1899. Middlebrook may also provide solutions to other problems. Because the paper clip made by his machine has double loops, which is very similar to the paper clip we use now. These paper clips are famous "Gem" brand paper clips. They usually don't damage paper. Now paper clips are made of plastics coated with different colors. This not only makes paper clips more attractive, but also allows users to "code" pages with paper clips of different colors. It seems that no one mentioned the patent of "Gemstone" brand paper clip, so it is impossible to determine who is its inventor. But since it was adopted at the beginning of this century, it has become a standard design.