Modified the original to fit my mirror from Daiso which was too small (143.6mm diameter, 1.5mm thickness). I made it into a more permanent mounting as well as a fixed bed leveler. After much trial and error, I made three different heights of the clamps 3.5mm, 4.7mm and 5mm for each mount point to cater for my grossly unleveled printer.
If you do not need to level the bed, just print the default 5mm version.
Wall Thickness 0.6mm
Top/Bottom Thickness 0.6mm
Printing thicker walls may cause some inaccuracies due to overextrusion
Print this standing up on its side.
Connect USB cable to view console and perform Auto Level from the printer
probe at 0,0 is -18.430000 mm
WARNING: probe is not within tolerance: 18.446663 > 0.030000
DEBUG: plane normal= -0.000917, -0.000290, -1.000000
Probe completed, bed plane defined