Use this to align the Ultimaker X and Y axes, to make them perpendicular.
This tool was cut from an alien bone. It wants to help you. Its true motive remains unclear. It's probably friendly, but replicate it at your own risk.
Print two bones, one of them mirrored (so you can mate them after use).
Loosen one pulley belt on both sides.
- Push the big and the small claw into the matching rods, on both ends at the same time.
Make sure you also have http://www.thingiverse.com/thing:8781 ready at hand.