See Mod from original
The author remixed this model.
As I printed and assemble the original model I found out that the profile wasn't perpendicular to the hub axis. I inspected and found out that it didn't touch the pretend axis (see pic). This is due to the fact that when printing internal corner are always a little bit rounded and not the profile cut. (True too for most internal machining).
So I redesigned adding a little pocket in the corner to let the profile go at the end of the tool.
Furthermore I removed the lateral holes as XY skew is possible (not corrected for example in he software of Prusa). It is better to rely in this case on only one axis.
I also increased the hole for the central screw as my 20x20 needed to be thread M6.
On top of this I designed a prolongation connector for the 20x20.