Final answer:
To flip and duplicate a group of bones on an axis, you should enter a value of -1 in the scale tool for the axis you want to mirror.
Step-by-step explanation:
To flip and duplicate a group of bones on an axis in mirroring, you should enter a -1 in the scale tool for the axis you want to mirror.
For instance, if you want to mirror along the X-axis, you would scale the X value by -1. This effectively flips the group of bones, making a mirror image on the opposite side of the selected axis. It's important to apply this operation to all relevant attributes to ensure the mirrored bones function correctly in animation or rigging.