"2HB" is a song written by Bryan Ferry and included on Roxy Music's eponymous debut album. He also recorded a version for his 1976 solo album Let's Stick Together.
The title is a pun - the song is not in fact about the European nomenclature of pencil leads, but actually dedicated to Hollywood film star Humphrey Bogart. ("2HB" = "to Humphrey Bogart".) In particular, it references the Bogart classic Casablanca.
The song is gentle and mellow in tone, evoking a smoky cabaret atmosphere and classic black and white films.
The instrumentation on the Roxy Music recorded is dominated by Ferry's Hohner Pianet N electric piano, and features a saxophone solo in the middle where MacKay's playing is treated with tape echo effects by Brian Eno.