Q. I am writing about pencils. The piece has to conform to CMOS. How am I supposed to write “No. 2 pencil,” which isn’t a proper name, but nearly so? If I write “Number 2,” it doesn’t seem to be “better.” Thoughts?
A. Where CMOS fails to offer a specific ruling, follow common usage. This often means looking to Merriam-Webster, but since there’s no entry there, you’ll have to do some digging.
Pencil companies seem to prefer the form “No. 2” (as on this page from Dixon Ticonderoga), though “#2” is also common. According to Google’s Ngram Viewer, those forms also happen to be at or near the top of the list of how such pencils have been referred to in books published since 1900. Book editors often default to spelling out abbreviations and numerals in running text, but even so, most of the spelled-out forms trail the abbreviations:
And though “number 2 pencil” would be okay with us—in line with “type 2 diabetes,” “size 10 dress,” and “type A executive” (see CMOS 7.89, sec. 2, under “noun + numeral or enumerator”)—we’d argue from the evidence above that “No. 2” will be more familiar to readers.
A third option—spelling out the whole thing (“number two”)—would be okay also (it’s the second most common usage). But as with dress sizes (and page numbers), a numeral matches what’s usually on the item itself.
As for the capital N in “No.,” there’s a close analogy in “No. 1”—as in “we’re No. 1.” That’s how “number one” in that sense is “often written” according to Merriam-Webster. It’s maybe not surprising, then, that the form “no. 2 pencil” (lowercase n) doesn’t even chart in an ngram (unless its absence stems from a limitation in Google’s data).
As most editors who work on paper would know, the “2” refers to hardness. A No. 2 pencil leaves less graphite on the paper than the softer No. 1 (which makes darker marks), but more than the harder No. 3 (which makes lighter marks). According to a more common classification system, a No. 2 pencil is an HB. H refers to hardness, B to blackness. So whereas an H pencil would be hard (and light), a B would be soft (and dark); HB is in the middle. These grades can also include numbers. For example, an 8B is softer than a 6B.
For more information on these and other details, see The Pencil: A History of Design and Circumstance, by Henry Petroski (Knopf, 1990).