Number 2 pencils: What makes them so special?

It's a staple on everyone's back-to-school list, but why do we always use No. 2 pencils? They really are the best writing utensil for the job.
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They're at the top of every back-to-school list, but does anyone know why No. 2 pencils are so important?

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What Makes #2 Pencils So Special?

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Number 2 pencils: What makes them so special?

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