I fixed the parametric file so it can work in FreeCAD Version 1.0.2 Revision 39319.

While at it, I also removed the hexagon-meshing, since it doesn't really serve a functional purpose and only makes the mount harder to print and take longer.

Step 1:
Download FreeCAD from here: [https://www.freecad.org](https://www.freecad.org)

Step 2:
Open the file “generic_10_rack_mount-SOLID.fcstd” and double-click the “Spreadsheet” on the left hand 

If you just want to adjust the model to fit your box you only need to tweak the first three parameters. Here's a brief description of the rest:

• rack_thickness: thickness of the rack aside from the front panel.
• rack_gap: margin added to the device width, height, and depth. I've found 0.5mm to be plenty to provide clearance without feeling loose
• offcenter_distance: shifts the mount off center left/right relative to the 1u plate
• hex_side: length of one side of a hexagon cutout
• hex_gap: distance between edges of hexagon cutouts
• hex_outer_gap: distance between outside of mount and beginning of hex cutoutsIf you just want to adjust the model to fit your box you only need to tweak the first three parameters. Here's a brief description of the rest:
• rack_thickness: thickness of the rack aside from the front panel.
• rack_gap: margin added to the device width, height, and depth. I've found 0.5mm to be plenty to provide clearance without feeling loose
• offcenter_distance: shifts the mount off center left/right relative to the 1u plate
• hex_side: length of one side of a hexagon cutout
• hex_gap: distance between edges of hexagon cutouts
• hex_outer_gap: distance between outside of mount and beginning of hex cutouts

Step 3:
Select “Final Body” and then File > Export in the top left corner. Then select STL or 3MF.