[itslow]

There are also (at least) two variations of the "heavy" axle, but "the book" doesn't make any note of it that I can find. There's the style with the indentations by the kingpin having squared-off top and bottom corners, which seems to be more common, and one where the indentation is rounded with no corners. The latter will obviously be easy to spot as not being reproduction once these axles are available, provided they aren't easily distinguishable from stock.