Shoulder Rig - compact middle_piece

The middle_piece of the 3d printed shoulder rig can be quite hard to print on smaller printers like the Thing-o-Matic.
(I printed the original rig on a RepMan.)
It's long cross-section may induce warping and it streches the limites of the build-platform.

This one is more compact.
It works for the center-support of the camera-plate, the counter-weight and the follow-focus.
2 additional holes in the shape of an M5 nut in the camera_place may be required to use this as the front and back mid