I needed (wanted, rather) an USB port on my bass amp to save me from hunting a wall outlet whenever I felt like using a pedal. 
All the panel mounts I could find did not tick all my boxes, mainly because the usb port I had was cut from an old derelict charger plus where I wanted it there was not enough room for any fastening nut. 

So I set out designing my own. 

Fastening is done via a wedge, it works in confined areas where a nut just won't fit. The design is printable without any support when oriented on the build plate as the model is provided.

Assembly: slide the usb mount into one of the halves, think first about the final orientation to make sure the wedge cutouts face the right direction. Slide on the second half, slip the ring over the assembly and install. Insert the wedge from the back and push hard :)

Installation needs a 18mm hole, the design works with panels from 1 to 3 mm, for thicker panels you might want to adapt the wedge and its corresponding slot (.step included). 

Update: added v2 to work with off-the-shelf 90° USB connector. Connector needs to be slightly modified, see photo.