Sometimes the wheels on the lower rack of a dishwasher break/fall off. The only replacements I've found are for the whole carriage, and not cheap. The snap-in peg will reattach a wheel, or if the wheel is lost/damaged, the wheel-peg combination will snap into place.
This one fits our old kenmore/whirlpool, which seems to be pretty common; check the measurements in the openscad file against yours and adjust if needed.
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