Hello everyone! I shared a video to better explain the problem: https://www.dropbox.com/s/bb96ih5xsq...10108.mp4?dl=0
By measuring a cylinder with the caliper I obtained these measurements:
x axis = 4.70 mm
y axis = 4.45 mm
diagonal 1 = 5.2 mm
diagonal 2 = 4.55 mm 0.5mm
difference between the widest and the narrowest point is a lot!
The curious thing is that if I print a cube it is precise!
I tried to pull the pulleys and check that the eccentric nuts do not let the plate wobble, the extruder and also the z axis is guided by a support that I have printed, at its upper end. What can it be in your opinion?

Slicer: Cura