This assembly uses twenty (20) of these POM idlers:https://www.aliexpress.com/item/3D-printer-accessories-10-pcs-dual-bearing-smooth-TIMING-BELT-adjustable-idler-wheel-delrin-POM-H/32392577798.html?spm=2114.13010608.0.0.drreTp
Turns out, illustrious Chinese comrades bored from both sides to leave a step in the center so the bearings don't push through. Good solution, yet creates a defect when you pass a bolt and tighten it, it locks up the bearings because they don't mate on the inner race.
Had to press out all the bearings, which breaks the center POM ring, good thing it's POM as it shears clean. Then reassemble with a washer/spacer. Sure the bearings may walk out (very slim), but at least they turn.