It's definately not a given as far as OBJ's go. As for these particular models, I suppose it would make sense fro ZYgote to make one half then mirror it. Just because they mirror in the x direction, they certainaly don't in the other's. Not familar with this program or what it does, but I would suggest at least giving an option for the user to specify the mirroring values themselves. Plus perhaps a transformation/rotation set prior to that. Many models come in many different orientations, and that's completely at the whim of whoever made them. So they could really be anywhere, although in general people do tend to keep them near the origin. Bruce