Two pieces: 1x3 (42 x 126mm) each
Building a gridfinity box that holds the box for a Mahr 16 FN caliper.
Thanks to @jdegs who provided the Filled-in Gridfinity Boxes (For Customization) that I used as a base for this model.
The author remixed this model.
Added cutout for the Mahr 16 FN caliper box.