Threaded Rod Parts Pack (revisited)
These have been successfully printed at 0.1mm layer height, 20% infill, and 60mm/s print speed. It also requires supports from build-plate.
The threaded rods are also successfully expandable, making up to 24" threaded rods possible.
The C in "CM" stands for custom, meaning these may not fit other M8 or M12 parts.