The number on a pencil indicates the amount of hardness or softness the writing core has.
A #1 pencil is very soft, makes a dark mark, and tends to smudge.
A #3 or #4 pencil is very hard, makes a light mark, and tends to “dent” the paper.
The #2 grade pencil makes a nice dark mark that is easy to see (or scan . . . for tests), is easy to erase, and doesn’t smudge.
Incidentally, pencils do not have lead in them. The writing core is made from graphite and clay. More graphite and less clay makes a darker mark – more clay and less graphite makes a lighter mark.
Oh, and the little metal band that holds the eraser on the pencil is called a ferrule, a combination of the Latin words ferrum (“iron”) and viriola (“small bracelet”).
The Graphics Lab has pencils, pens, and markers available for your use – no need to bring writing utensils!