I have missed something during the VAT-Frame build. Someones sharp eye pointed it out.
Between the U shape profile VAT base and the L shape sides of the VAT frame there are small screws that protrude.
It is a set screw with a M4 collar. It is used to set the VAT to be parallel and at a specific start distance from the build base.
This is what it looks like only smaller:
The inside diameter is M4, but the screw itself is M2.5 thread. The bolt is 30mm x M2.5
Sorry! and Thanks for pointing that out.