This is a small dial Indicator holder thats bolts on the front of your Prusa carriage using the fan holes.
This will help you level your build platform.
I have added one that lift the dial Indicator higher and closer to the carriage.
Simply print and bolt on using 2 x 5/16"x 1" bolts, M4 x 25mm to lock the dial Indicator in place. Don't forget some washers.