This modification mostly applies to early V1 of the Duplicator i3. Later V1s as well as V2s have a second set of mounting holes to mount the Z stop switch higher to accommodate a 1/8″ or 3mm glass bed. However, you may find this still does not raise the switch high enough.
You may find that you cannot get enough distance between the nozzle and the bed after adding glass to your bed surface. This can usually be remedied by moving the Z endstop to the top set of holes on newer models or print one of the many adjustable or Z endstop adapters from Thingiverse.
Built this to accomplish two things. First, raise the default end-stop position high enough to allow my 3mm Borosilicate glass to fit. Second, I wanted a way once I had everything level to do very fine adjustments to the Z height. This would allow me to switch out different glass or other materials (garrolite for nylon if we get an all metal hot end), etc.