This is a simple interface between a flat surface (roughly credit card sized) and a GoPro compatible mount on the other side.
Note: The interface replicates the camera side (i.e. the GoPro side only has two tabs), not the fixture side (which has 3 tabs and holds the M5 nut).
Cell phone mount

I used this to create a simple cell phone mount by gluing a silicone phone bumper to the flat side. Using cyanoacrylate glue might not have been the perfect choice to bond the bumper's silicone (?) to the ABS as it took quite a while to set (I did not use an accelerator) and the evaporating CA fumes discolored the black ABS, becoming slightly grayish.
The mount has three through holes in between the GoPro interface and the flat surface (two are parallel and shown in the picture, the third one is perpendicular to them). They are meant to hold small cable ties so that you can route any cables going to your phone closere to the pivoting joint.
If you don't use a flexible silicone bumper, but a hard case, I think this should be strong enough to hold a 7 inch tablet as well.