The hardness of pencil leads is generally indicated by "H" for hard pencils, "B" for soft pencils, "HB" for medium-hard pencils, and "F" for pencils with a hardness between HB and H.
The hardness grades are arranged as follows (from softest to hardest): 9B, 8B, 7B, 6B, 5B, 4B, 3B, 2B, B, HB, F, H, 2H, 3H, 4H, 5H, 6H, 7H, 8H, 9H, 10H, etc.
The larger the number before "H," the harder the lead and the lighter the color. The larger the number before "B," the softer the lead and the darker the color. Pencils are classified according to the amount of graphite in the lead. H-type pencils have relatively hard leads and are suitable for drawing on relatively hard or clearly defined surfaces, such as woodworking marking and outdoor sketching; B-type pencils have relatively soft leads and are suitable for drawing and also for filling in machine-readable cards.