Parametric Ball Bearing

The inner and outer rings of a ball bearing. The inner ring is separated into 2 pieces that press-fit together. (gluing optional)

It's not an exact replacement for a ball bearing, but it could work as a temporary replacement for a broken bearing, or in a design that doesn't require much durability.

To assemble, place the bottom of the inner ring in the middle of the outer ring, push the metal balls into place, then attach the top of the inner ring.

I've included the OpenSCAD source, plus an example 628 bearing that uses 12 1/8" metal balls.

The relevant parameters are listed below. By default, the gap between the two rings is centered between the inner and outer rings. 

od=24; //outer diameter
id=8; //inner diameter
h=8; //height
bd=0.125*25.4; //ball diameter (1/8" or ~3mm)
ct=12; //number of balls

clr=.6; //gap between inner and outer rings
clb=.1; //clearance around each ball