A replacement for the smooth idlers that come (or used to come) with ORD Bot kits. It fits the same two bearings and is a drop-in replacement.
Slice with 2 perimeter layers @ 0.30-0.32 mm skin thickness, layer thickness 0.15-0.17. 50% infill worked fine for me. Print two at once if your cooling is not up to the task.
Why replace the original idlers? Well, for one, because they have a flat lip instead of a conical one and cause the belt teeth to rub and clip against the edge. Also, because they tended to cause belt slippage upwards, which made the belts rub against the bottom of the Y plate.
This is the GT2 idler, if someone needs an MXL, let me know and i'll make another version.