I had some loose wrenches in my toolbox. 

This model holds six wrenches tightly, so that they don't fall out when turned over, but you can separate one easily. The amount of filament is quite low (~25g).

The STL model itself is probably useless because you will not happen to have the same wrenches as I do. But the attached FreeCAD file is somewhat parametric. It has a spreadsheet were you can insert the measurements of you wrenches thicknesses. This will place the cutouts nicely. Maybe you need to adjust the size of the body a bit and redo the fillets.

The example image was printed with:

• 4 walls
• 15% cubic infill
• Material4Print Tough PLA (made in Germany)

Feedback to better FreeCAD practices is welcome in the comments :-)