We sometimes have customers who ask us which of our mechanical pencils are "No. 2". Great question!

Pencil leads have different levels of hardness or softness for different uses. You can read more about this in our PenPedia article Picking the Perfect Pencil Lead Hardness. For mechanical pencil lead, the leads are labeled (from hardest to softest):
9H | 8H | 7H | 6H | 5H | 4H | 3H | 2H | H | F | HB | B | 2B | 3B | 4B | 5B | 6B | 7B | 8B | 9B.

The numbering system for wooden pencils actually refers to the same thing, but uses an American labeling system. For example, the equivalent lead hardness for the following wooden pencils are:

American Numbering	World Numbering
#1	B
#2	HB
#2 1/2	F
#3	H
#4	2H

So using a mechanical pencil with B leads should be equivalent to using a No 2. Pencil.