Boolean failure

Hi to everyone … sometimes like now it happens to me not to use well Rhino. I can not boolean together the 3 parts in the design. I have tried unsuccessfully many times. Anyone can help? thanks in advance. Mirco

attached rhino file
19 april.3dm (17.1 MB)

I would first try to fix symmetry.

those 3 surfaces are not planar.
They form a Boundingbox with 0.001 mm thickness… (green)

If you re not relying on the 0.001 mm Tolerance.
set the document Tolerance to 0.01 and BooleanUnion works fine here.

thank you very much, I have done it. !