The post on the magnet holder on my Park Tool chain scrubber snapped off, so I measured everything and designed a replacement. It fits mine perfectly with enough tension that it won't fall off but I can still pull it off if needed. If yours ends up a little tight or loose, I'd say scaling the X or Y just a little bit might be easier than messing around with your extrusion settings.
For maximum strength, you'd want to print with the post horizontal and supports from the bed. I printed mine with the post vertical so I didn't have to bother with supports and it still takes a reasonable amount of force to break it.
The author hasn't provided the model origin yet.