Try our new info resource - "Aladdin's Cave" (Main menu)Just added a separate link to Ash's Dropbox thread (shortcut)
According to the CMS parts book Ash the 500 and the 550 both use the 750 front spindle, 300 middle part number. For a minute there I was thinking you were saying the 500 was a solid bar with the 550 being hollow, couldn't remember if that was true or not so looked it up.
Yeah, I looked at the F1 book Ash, TBH I didn't expect the F2 to be different but it clearly is. You could be right as the F2 spindle should be the same as the K3 spindle and that has that odd looking end on it. Still fitted wrong though and needs to be corrected asap.
Just to clarify, we are talking about the black 500 not the gold one. A look at the gold one, from the nearside, shows that if fitted correctly the spindle actually extends just outside of the flange on the nut.