Filament spool 52mm to 8mm adapter

With my Anet A8, the filament spool spins on an 8mm rod. This results in jerks on the filament as the spool swings around loosely. To fix it, I designed a simple adapter that sits inside the spool and centers the axis of rotation around the rod, resulting in much smoother filament feeding.

UPDATE:
The two halves of the adapter can end up separating, because one of the the M8 nuts will end up being moved along the rod as the reel un-spools. To stop this, I designed this simple spacer to take