at what point in time did jones measure? arnold went through so many weight gains and losses, those arms could have ranged from 17 1/2 to 21 at different times... look at some pics where he is really small (compared to his prime), and others where he's huge.
could've been 20 in contest shape, or a shade under, arnold was huge, but also a master of illusion, for example he didnt have great abs nor a small waist, but ALWAYS was aware of his midsection, and never relaxed it, always sucking it in, his lower abs were not great
also not many if any pics of arnold doing an abs pose...?
btw, what would franco's arms have been at their biggest? a shade under 18? very muscular and defined, but probably 18 max