I often create parts that need to be mirrored and I come up against the same problem all the time. I select the part, select the plane that would reflect the part best and when I click ok, the part is usually just rotated 180 degrees and duplicated. I have clicked the Next arrow to select the part orientation that I am looking for, but the other orientations don't work. It's like I'm looking in the mirror and can choose to see myself standing on my head, standing on my head looking at my back, or looking at my back standing upright, but not a normal reflection.  This problem isn't specific to just one part or assembly. What am I doing wrong?