These are named "mechanical pencils" in English, but some other languages use the term "lead holder" (eg. French : portemine). What word in esperanto would be the most understood?
By coincidence, we were discussing this very question on Facebook in the Lingva Konsultejo just a few days ago. While PIV lists ĉukkrajono and puŝkrajono several people commented that these terms were not clear (especially before it was clear that I was quoting PIV and not simply making them up.)
The only alternative which was made was "reŝargebla krajono" - which seems OK to me. It seems you could also call it "reuzebla". In spite of what it says in PIV, it doesn't seem like there is a single stable term for mechanical pencil.
According to PIV: ĉukkrajono. Puŝkrajono, kies grafitaĵo estas tenata per ĉuketo.
These days the distinction between krajono and plumo is somewhat outdated and artificial. They all are skribiloj. This is also reflected in some languages, where all are called skribiloj and only if necessary, a defining part is added. Esperanto works that way on many cases by preferring compound words and adjective attributes instead of separate words.
- grafitaĵa skribilo
- reŝargebla skribilo, ŝraŭbskribilo, puŝskribilo