Fine detail:- over many years I've collected several maintenance bike books, one was when I was in USA early 1990s another book published by Haynes a well known UK maintenance book publisher, both these have exploded views showing it to be an axle, whereas other books I have don't / so its really not a big issue, like nowadays you put a speedo on your handlebars & call it a cockpit ! times change why worry in my retirement.