Where does “HB pencil” come from?

HB pencil (English) comes from English pencil, from Old French pincil, from Latin pēniculus, from Latin -culus, from Proto-Italic *-kelos — Diminutive suffix.

Ancestry of “HB pencil”, step by step

HB pencil traces back through two separate lines of ancestry.

via English pencil

StepLanguageWordMeaning
1EnglishpencilA paintbrush
2Old Frenchpincil
3Latinpēniculus
4Latin-culusAlternative form of -ulus; added to a noun to...
5Proto-Italic*-kelosDiminutive suffix

via English Hb

StepLanguageWordMeaning
1EnglishHb(describing a pencil that makes lighter marks than a grade B, but darker marks than a grade H pencil)
Every word from Proto-Italic *-kelosEvery word from Latin -culusEvery word from Latin pēniculus