The main component of the pencil lead is graphite. In fact, the refill of the pencil is made by mixing graphite and clay in a certain proportion. For example, “h” is the prefix of “hard” in English, which represents the content of clay and is used to indicate the hardness of the pencil lead. The larger the number in front of “h” (such as 6h), the harder the pencil lead, that is, the greater the proportion of clay mixed with graphite in the pencil lead, the less obvious the written words, and it is often used to copy. “b” is the beginning of the English “black” (black), representing the content of graphite, used to indicate the softness of the pencil lead and the obvious degree of writing. Ordinary pencil marks are generally “hb”. The pencil mark used to paint the answer sheet during the exam is generally “2b”.
The main components of the lead core of the pencil are graphite and clay. According to the national standard, pencils are divided into 18 models according to the graphite concentration. In the current standardized test in our country, the computer can only read the pencil handwriting with a lead concentration of 2B. Too thick or too light will cause the computer to fail or error in reading.