Erik, you're not alone in thinking that HB is a brand name, but it's not. As Andrew explained to Andrew F. above,
Originally Posted by Mark McDonnell
HB is more a categorisation than a brand name. I was going for something deliberately generic and mundane that the characters would be familiar with from their school stationery, where all the pencils are marked HB (or 2B, 3B etc). I don't think they would recognise the smells of an individual wood like cedar.
HB is written on a lot of pencils, but isn't a brand name (like Ticonderoga or Blick). It's a softness rating. I think in the United States the emphasis is on the "No. 2" part of the "HB No. 2" rating, rather than the "HB" part. But answers on fill-in-the-bubble type tests at school might not be readable by the correction machine if students use pencils with any other softness rating than HB No. 2.
I think the inclusion of "HB" does a good job of communicating that the two principals of this drama are still school-aged.