Just purchased the QRP and a camera plate from NN, but am I thick, or what? How the heck does this go together? I can see how the QRP attaches to the upper rail, and then how the CP fits the QRP, but then how does that, in turn, attach to the bottom of the camera? I have two female 3/8" threads that meet together. Also - why does the CP have to 'lock' into the QRP when the mount, with the screw and the alignment pin are bomber secure to start with?

I must be doing something wrong - or there is yet another piece I have to buy between the camera and the CP.

Camera is Nikon D300