Originally Posted by katyquilter

I'm about to try a plastic bobbin in my 99K which I recently purchased at a thrift store. It came with one metal bobbin and I bought the metal 66 bobbins which should work. they fit but do not work - the machine refuses to sew, it's as if the bobbin is just a hair too tight. So someone suggested plastic. I'm going to have to get some to try soon unless someone has a better suggestion.