This is just a bottom model of a backpack hanger. I designed for my wheelchair because I need something to hang my backpack off of. It works great and it can be customized to whatever you plan on attaching it to and hanging your backpack off of.

All you need to do is attach for different M8 screws and nuts, as well as a knob with a M8 50mm threaded knob for attaching the hanger component & M8 nut to tighten it down to the side mounts,