Ultimaker anti Z wobble

Z axis on ultimaker is kept only by the bottom coupler and could, in few cases, show some lateral movement that is compensed by the movemment in the XY plane of the Z brass nut.
Just to be on the safe side, this little object can help to keep the upper end of the Z threaded axis in place removing any residual off-axis movement.

int the 2nd picture, on the left the printing of a test box 25mm high, WITH the anti_z_wobble, on the right the original print...