Most of our pencils come with a black graphite insert or core, each with their own xHB two-scale rating. The first grading scale is a number. The higher the number, the harder the writing insert/core and the lighter the mark left on the paper. The second graphite grading scale is known as the HB scale, with the letter H used to indicate a hard pencil and the the letter B the blackness of the pencil mark left.