This is the bottom half of the ESC bracket. Each ESC sits inside this bracket, with the power leads going to the centre. The four pillars in the centre are for mounting the power distribution board.
You can download the .stl or Freecad files here;
Don't have a 3D printer? If you are in the UK you cano order one from civrays via makexyz.
Please check out the other 3D parts;