A class 15 bobbin case is the one that fits-I dug out my extra. I have no idea what the black ring was. The machine did sew with it on, but not well. I suspect the previous owner lost the case, used this as a stopgap, then ditched the machine when that didn't work well. That's a WAG, obviously, but the machine was otherwise clean and running well, so that's what I'm going with. *g*