Drawing pencils come in a variety of types that have different features depending on the intended use and harder pencils create lighter marks while softer pencils create solid, dark lines. Artists normally use different grades of pencils for shading and drawing sketches by hand.
The grading system for artist pencils used a numeric and letter code to indicate the hardness or softness of a pencil. The higher the number, the harder the core. The letters represent hard (H), blackness (B) and (F) to indicate that a pencil has a fine point.
Drawing pencils contain lead and a filler and this ratio is responsible for the harness of the writing tool. Since there is no industry standard, its best to test new pencils before buying them.