This is my design for the spool holder design challenge.

This is a hook designed to attach to the wood shelf quickly and easily.

The hook is designed to swing away easily and to lock into position when the arm is either folded to the side or pointed outward when in use.

I've added an extra long version of the arm... so everyone can customize the lenght they prefer. With some Slicer software if you print the arm vertically... you can partially sink the model below the print bed and any part below the print bed won't be printed. So by varying how much of the model of the Arm is above and below the bed will decide how long/tall the arm will be printed.