Backpack hooks

This is a set of hooks I used in both my Space Marine cosplays. You'll need at least two sets (although I recommend three, arranged in a triangle) for a stable connection.
There is only one "hook", but the receptors for that hook come in three variants. The two smaller ones just have a different hole pattern (I had to update them for my second Marine), the third one is wider to clamp down foam with it.
There are holes to bolt each piece in place, as well as holes (I believe it was 5mm) to put magnets in, to prevent accidental loss of backpacks.
That said, the magnets were overkill. While there is clearance in the models, you can probably just use friction to keep whatever you mount with it in place. Additionally, depending on how you space each receptor relative to each hook, you can also generate friction as needed.