I created this Z-axis brace to help maintain the squareness of the Mini once you get it dialed in.  I wanted a brace that mounted to the outside surface of the Y-axis extrusion.  All the others I found mounted to the top surface, and was “difficult” to access the hardware while the heat bed was in place.  With this brace all the hardware is easily to get to when needed.  

Hardware needed:  

4x M5x16 Button head or Socket head screws

4x M5 T-Nuts

1 Brace (I printed mine using Prusament PETG with 5 outer walls and 25% infill)

Before installing the brace make sure your mini is square by following instructions here:

https://help.prusa3d.com/article/xz-axis-skew-correction-mini_158518