This is a fully parametric 3d-printable thrust bearing cage, using cheap ball bearings to provide reliable motion. I needed a thrust bearing in a weird ID/OD combination for a low-load situation, and couldn't find anything reasonably priced off-the-shelf.  Total parts cost for the attached size is <$4 including filament.

The model parameters can be adjusted to change:

• Inner diameter
• Outer diameter
• Total thickness
• Tolerances
• Ball bearing size

The attached STL is a 40mm ID/110mm OD, using 36 ¼ inch ball bearings. The balls pop into the bottom part of the cage, and are fully retained once pressed in, while still being able to rotate freely.

I used PLA to print these, due to its stiffness compared to PETG. 0.2mm layer height is plenty of detail for the radii in the bearing cages, but the bearings might run a little smoother with smaller layer heights.