The original wheels for this folding shopping cart from Target (under their “reusable bags” brand) were made of flimsy foam and thin plastic attached with a bobby pin. When one of them broke, I replaced them with a pair of robust wheels from the local hardware store, with 3D-printed bearings to match the difference between the cart's 7.5mm axle and the wheels' quarter-inch inner diameter. I also designed my own more robust replacement for the pin-and-cap assembly that keeps the wheel on the axle.

There were also some horseshoe-esque “feet” on the outer bar that had broken or come off: I designed a replacement for that part as well. The one that came off seems to have been on a narrower part of the bar, so I tightened up the “shoe” design by one millimeter from the measurements I had of the piece that had stayed on: both versions are included here.

I've been using these parts for a few years, and haven't run into any issues yet. (The foot replacements are more recent, but they don't seem to be any less resilient than the ones that came with the bag.)

Print and assembly instructions

Print one cap, pin, and bearing for each wheel. Slide the bearing onto the axle, then the wheel onto the bearing. Finally, place the cap on the end of the axle (flush with the very tip), and slide the pin into the carved out tunnel in the cap: it should grab onto the narrower part of the axle where the bobby pin was originally.

All of these are oriented how I printed them on the bed: the bar-shoe requires supports for the inner peg that goes in the holes of the bar (PrusaSlicer 2.6's “Organic” support structure works great).

I recommend that the bearings and shoes should be printed at 100% infill: a draft shoe printed with the default 15% infill broke the second time I ever took the cart out.

I printed all of these in PETG: other materials would probably work, but I'm not sure I'd risk the brittleness of PLA.

Sources

The parametric OpenSCAD source files for these parts are available on GitHub.