Originally Posted by QBeth
Did Singer say why the pre-wound bobbins won't work? Interesting.
A size L bobbin is not the same as a size 15J bobbin. That's why it won't work.
If you have a class 15 machine, you can use a class 15 prewound bobbin.
A class 15 is not the same as a 15J bobbin, so that would not work for your 15j machine, either.
Bobbin classes must match exactly. 'Close' is not good enough.