Prints as two seperate parts that should simply clip together and fit very firmly!
To attach the bracket to the shelving simply grasp the comfortable grip, hold with the clip and button on the top, and push the bracket onto the shelf in the desired location.
To remove the bracket simply press the button above the grip with your thumb.
The bracket can acomodate two spools simultaneously, one on either side. ( I hope )
( As I currently find myself without a functional printer I have been unable to prototype this, confident it will work. I have only rotated the object for the picture, the file is flat on the bed, some supports needed. May I suggest printing in PLA or some other semi flexible material (nothing brittle) Hope to see you test this in the near future! #highfive )