The most used and common grades of pencil are illustrated in the diagram Below.
On the left of the diagram are the most common for pencil portrait drawing.
The numbers and letters are part of the grading system to signal the type of lead that is inside.
The letter ‘H’ means ‘hard’. This kind of lead is hard, which doesn’t add a lot of lead to the paper, keeping the shading very light. The number next to the letter tells you how hard the lead is with 9 being the hardest and lightest.
Pencils with an ‘H’ gradient are generally unused in pencil portraiture, simply because the lead is too hard to manipulate on the paper.
The letter ‘B’ means ‘bold’ or ‘black’, and signals a soft lead in the pencil, which adds a lot of lead to the paper, creating darker shades. Similar to ‘H’ grades, the number next to the letter signals how soft the lead is, with 9B being the softest, and therefore darkest.
These are the most common in pencil portraiture.
The ‘F’ grade means ‘Fine point’. These pencils are still relatively hard, but have a very fine, sharpened point. Again, these are uncommon in pencil portraiture.
And finally, the good ol’ ‘HB‘ we all doodled over our text books with in nipper school. This is half-way between hard and soft, and is neither here nor there. Some pencil artists may use this pencil for crating lighter shades, though I personally find it still a little too hard.
If you did choose a set, then odds are you will have a good portion of the grades set out above in the diagram.