OK from the outside in, there are:
A) The track nut.
B) The thing in the inside that clamps against the fork
C) The Mystery Piece
D) The hub.
What is the Mystery Piece? Is it part of the hub? Or is it a spacer?
I ask because the hub (as is) won't fit inside my fork. Removing the two Mystery Pieces (one on each side) would appear to make it fit perfectly. It's a steel fork so I don't have too many qualms about just forcing it on in there, but if I can de-space it that would be perfect.