16014 BB Bearing

I needed a bearing for a project, didn't feel like buying one, and nothing already here fit my needs correctly without having to buy special hardware.
So, for a low-speed low-stress use-case, I put together this for use with 6mm airsoft pellets, and thus far it seems to work just fine.

You'll need at least the outer and inner races, and the cage, which if your printer's got decent tolerance you should be able to print concentric in one go. The assembly ring is optional, but makes putting the bearing together slightly easier.
On top of that, you'll need a dozen 6mm airsoft pellets, and a pointy object (screwdriver, tweezers) to push the pellets into their right positions.