This is another one of those interesting “Gretsch-isms.” As part of the company’s marketing strategies (because Gretsch guitars were the most expensive of all the top name-brands), it would give certain standard features interesting names. “Actionflo” was a term used to describe the neck on the Chet Atkins line and appears to refer to the addition of a zero fret behind the nut. Chet had some concerns that the plastic nut may have been hurting the tone of open string notes and chords, which led Gretsch to add the zero fret. Thus a 21-fret neck actually had 22 frets. In other ads and literature, Gretsch seemed to also use the term Actionflo to indicate the neck had a truss rod, which could be adjusted to slightly raise or lower the action on the neck.