Yes, there are – Mental Floss answers that and everything you wanted to know about the ENTIRE SCALE of pencils …

2B is known as the #2 pencil. B is the #1 pencil.

So why are testing centers such sticklers about using only No. 2 pencils? They cooperate better with technology because the machines use the electrical conductivity of the lead to read the pencil marks. Early scanning-and-scoring machines couldn’t detect marks made by harder pencils, so No. 3 and No. 4 pencils usually resulted in erroneous results. Softer pencils like No. 1s smudge, so they’re just impractical to use. So No. 2 pencils became an industry standard.

You can read more at Mental Floss.