You have an unusual bit of Singer history. Singer bought Wheeler Wilson. And started using their factory before they moved Singer parts in. They used Wand W parts and rebadged them as Singers Maybe a few other changes.That's one reason it doesn't have a boss WW hand cranks ( if any) would not have used Singer mounts.
I don't believe it shares a bobbin with many, but I'd be glad to be shown the error of my ways.
My W W follows..