Retention clips?

I've been looking at these retention clips here and how they are used on the caselabs cases, but I don't see the other parts to the clips, or maybe I'm just not getting the function of these... http://www.caselabs-store.com/replacment-retension-clips-10pk/

I have a use for this system, but I don't know where to look to find all of the pieces to the clips, and not just the clips themselves. I have a feeling that the reason they only sell the clips is because the actual piece that locks in to the retention clips is part of the aluminum panel itself, therefore it would be impossible for them to sell those pieces separately, obviously.

Anyone have any suggestions for this? I need these retention clips or something like them in order to really work with the frame I have right now.