Originally Posted by vintagemotif

Okay, I couldn't wait until evening. It's my lunchtime; so, I took some pictures since it was faster than trying to figure out where my post is located. Singer Class 66 bobbins have a curve to them while Singer Class 15 bobbins are flat. The newer metal bobbins that are sold don't always work correctly since they are poorly made. They are either warped or the center moves around so that you can't wind them. Plus, some sit higher in the bobbin area, so they will not work well either. Look for vintage metal bobbins since they work! Hope this helps ya!