This would also work on a metal file cabinet.
Step 1: Tools needed
Drill (mine is dremel)
Picture hanging hooks
Magnetic Hooks (bought on ebay holds 20 lbs)
Step 2: Prepare Thread Holder
Step 3: Attach picture hanger
Step 4: Place magnetic hooks on cabinet
Place magnetic hooks on side of cabinet (if that is where you want them to hang). Don't worry about being exact because with magnetic hooks you can move them around. The ones I bought are very strong and it takes a bit of effort to move them. If I had it to do over, I would have glued a thin piece of felt on the back of the hooks because when I move them, it feels as if it will scratch cabinet. I did not see any damage on my cabinet, but still it would be safer to glue thin felt on back.
Step 5: Attach thread holder to cabinet.
You might need to bend back the picture hanger hook a bit to manipulate onto the magnetic hook. At that time you can slide the magnets to be in line with wooden thread holder and your attached hook.