I had a problem with my bobbin rattling around in the case. The 15 class bobbins don't fit my machine (even though they're supposed to). I had a heck of a time keeping the thread from jumping out of the slot and going kerflewy. I put a piece of that purple stuff that marks the seam line. It's pretty thick so I just stuck it on the bottom of the bobbin and dropped it in. It makes the space smaller top to bottom. Works like a charm.