Here is another pic that shows this a little better:
So the thunderhex shaft goes through both sides of the 2x1 tubing. This means when you screw into the standoffs to mount the plates to the frame, the standoffs cannot rotate because of the hex profile machined into the tubes for the holes.
There are trapezoidal shaped cutouts in the frame tubes to fit the module. This was done to get the wheel as close to the edges of the frame as possible (the center of the wheel is 2" from each frame edge). Maximizing wheel footprint was an important point for us. We are able to cut most of these cutouts easily on our Omio, and then finish the cut with a bandsaw.
If you had to replace an entire module (should not happen), you would remove the 6 screws from the top plate and the entire module would come off from the top and bottom, with the thunderhex standoffs sliding out of the tubes with the bottom plate. You could also do the reverse, but then the turret would also become off the bottom plate.
Generally we have found we never ever have a need to pull an entire module. This design has made it really easy to service (1 screw pulls the wheel, 4 screws pulls the entire turret pod).