Made a set of cheap roller to see how much I enjoyed riding them. I made them from 3 inch ABS pipe fitted with drilled end caps that were fitted with lag bolts. The lag bolts fitted into skateboard bearings that were resessed into the 2x4 frame.
This build was meant as a test of the design but worked well enough that a second version was built. The only issue was that I triangulated the center of the caps with only a tape measure and hand drilled the holes which made the rollers wobble slightly at high speeds.