That is definitely one of the strangest designs that Ford put out for something so simple. 250lb fthas been enough for designs dating back to the 1960s. Almost as if they got something wrong and just went with just keep tightening it.
Not only that but the 4wd's use a tiny (M8?) bolt in the end of the axleshaft. It's clearly just there to keep the shaft from walking in and nothing more.
