Threaded rod, nuts, and knurled sheath for a pair of standard ~1.1 inch center hole, ~5 pound weight plates.

The nuts and knurled sheath are scaled to 104% in the x and y directions with respect to the threaded rod, to make them easily thread onto the rod.

After assembling with weight plates, be careful not to drop the whole assembly, as a sudden shearing/bending force can snap the threaded rod.

I also threw in a cradle I designed to stop the thing from rolling on the floor. I just glued it directly to one of the two weight plates.

Designed in OnShape: https://cad.onshape.com/documents/1db4e75d741d4b34bc496ff0/w/d05f0f4c010dc68efacca585/e/9f2b70fbfd2b0661b6b27139

Print instructions

To slice, use the "split > to objects" option in Prusa Slicer, to select which sub-objects to actually print, then use the "cut" function to split any of the objects at desired z height--all threaded objects will thread onto the shaft when cut at any height. For example, the knurled sheath is likely way too long for any use, and needs to be cut at 90 mm or whatever one's fist width is. And the nuts are likely excessively tall, and can be cut in half to make more room on the threaded rod.

To print, use a high infill percentage for the threaded rod. Most other settings are just "whatever works for your printer". I did a 0.2 mm layer height in PLA, but ABS or PETG might be even better, and 0.3 layer height would probably also be fine.

I also used a raft and brim on the really tall parts to stop them from detaching and toppling.