I rebuilt a plane for a guy with jr arms( I think coulda been Hitec or Futaba now that I think about it), and they didn't fit the atx servo's that I used in it. Possibly one or the other changed, but I don't think atx has. Don't get me wrong, it fit, it just didn't fit right. Are you looking for a certain size. Perhaps I can help you find something.

BTW, standard atx size servo's that I've used all use the same spline setup.