I needed to put my webcam for Octolapse on the front acrylic panel of my printer box so I came up with a plate with a screw to attach the cam and some double-sided tape, but I disliked the way that it lets some glue to the acrylic and stay locked in place so I imagined this version with magnets ! Which can get double sided tape too ! (for non magnetic surfaces, e.g. walls)

With 4 10*10mm cubic neodymium magnets it holds very firmly in place, I think it can support devices up to 200g without any problems.

Needed:
-Round 10*3mm neodymium magnets (5mm max thickness)

-One hex M6 screw: you need tu cut it at the correct length that will fit your device(10mm in my case), I don't have any 1/4 screws at home but if you don't tighten it too much into the threading, it'll be fine. (feel free to post a remake for 1/4 screw or ask in comments, I'll try my best)

-4 other magnets for the other side (if you want to use the same round magnets, I recommend to double them at least).

I recommend to put a tiny piece of paper to protect the plexiglass from scratches with the magnets on the outside side (especially if you want to replace or slide it).