Most of my machines us a standard 15 bobbin. I have one that does not and it needs a bobbin that has a bit of a curve to it. I am watchful now that I know this to insure getting the right #15 bobbin to fit it. My Janome does not like other size bobbins and always plastic in this machine. Oh yeah I forgot about my Featherweights they take a totally different kind and size of bobbins.