I have 3 machines, a Featherweight, a Janome 1600p, and a Bernina 830 Record. They each use a different size metal bobbin but the bobbins look very similar. I don't have many bobbins, 5 - 10 per machine. Any tips or suggestions for making sure I don't mix up the bobbins and put one in the wrong machine? Does any one mark bobbins - like with a dot fingernail polish or a marker?