It is protective/mounting bracket for small Dell speaker from Optiplex machines.
I am using them as small speaker for any arduino projects(talking robots, etc).
It is nice small speaker with 5V amplifier build-in and it can be very loud:)
I am saving them from old faulty computers, do not let anybody to put them to the scrap:)
Fusion360 files attached if you want to modify it.
There is few version of speaker holder, print it and try which will fit best.
Prusa i3 MK3
no support(supports included in model already)