I bought a box of 100 bobbins and gave half to my friend who has a Bernina and I have the others to use in my Singer 15-91. The one that was in the machine when I got it has a notch on the inner ring and 1 small hole to the outside. The ones I purchased has 11 holes around the ring and a notch on the inside. will send a picture of them.
the top one came with machine, other I purchased off EBAY
[ATTACH=CONFIG]233101[/ATTACH]
they both fit my Singer 15-91
[ATTACH=CONFIG]233102[/ATTACH]