This device is used to pull filament from the spool on demand and provide a "buffer" to ease the job of the extruder and prevent issues with spools that are far to the side.
It is completely independent of the printer.
Note that there are 2 types of clamps for mounting. One is for a square rod and the other for a round one. There's a screw hole in the base of the main section to allow you to fit a mounting system of your own, use mine if they fit your needs.
I've written a post detailing what I did, how and why. There are a lot more photos, a demo video and the circuit diagram. check it out: