I keep thread spools on those hanging, wooden spool racks (Joann's or Fons/Porter). The pegs on the rack are short so I bought some of those long toothpick/skewers that are about 4 inches long at the grocery. When I put the thread spool on the peg, I insert a skewer and then I can add the bobbin(s) to the top of the thread spool, keeping them all together.