Use in place of the bar clamps that clamp the Z-axis smooth rods to the bottom centre rod. Pop a 608 bearing into the cup. Use the end caps on the z threaded bar.
Especially handy if you use the alloy flexible couplings, which shouldn't be taking much weight.
Even more useful if you happen to have a stonking great X-axis motor which weighs a ton.

The scad code's a mess... quick lash-up job, probably won't scale very well so reluctant to call it parametric until I tidy it up, but for the standard iteration II Prusa it's fine.

Enlarged the cup hole so the threaded rod end stops don't grind in there.