It does use a 66 class bobbin and the ones you buy now are from china and are junk. If you buy ten you will throw
three away. Put each bobbin down in the bobbin case and see that it rotates freely and you can wiggle it around.
The bad ones will be snug or tight. The plastic bobbins seem to be better and stay loose. If you have a bad bobbin
then every time you put that bobbin back into the machine it will jam. It is best to check your machine with a known
good antique bobbin. Then keep that one just for testing when you suspect possible bobbin problems. Make sure the
exact same type of thread is being used on top and in the bobbin. If you don't you will have tension problems. Some
machines also don't like thick thread and you will need a big needle.