This spacer is a derivative work of Thing 14548. I've created this derivative solely for the purpose of providing others with an OpenSCAD description of the part so that they can fine tune it for their particular printer and bearings. That way, a good fitting spacer which won't rattle can be produced.
Also these spacers can be used on the Y-axis carriage as well as the Z-axis. As with the Z-axis, you would be replacing the press-fit adjustable bushings with these linear bearings.