This little things makes it much easier to adjust your printbed. The butterfly nuts are not the best way to do this, they are too big on the upperside and on the lower side, lead to jams by blocking the stepper motors. Just change the nuts to the upper side and use this socket wrench to level your bed by using it to turn the nuts on all four corners. Remove it after leveling. Done with freecad, you can download the stl-file or use the freecad-file to do some changes.