Edge on the Pinhole

[Xaratas]

I have found out that one of the holes in the sleeve of my green revomaze has an edge. (wenn das die richtige Übersetzung für Grat ist)
The core cannot pass freely while it slides, without the pins, through the sleeve. But how to remove the edge? It's minimal, like 0,01 mm, but big enough to hinder the movement.

*edit*
Softly use of a pencil with a piece of sandpaper attached to it with double sided tape removed the most of the blocking edge.