The original bobbin was one the store wound and put in and I'm not sure what brand it was. But I ran out and started using the Janome bobbin thread that came with the machine and apparently it's slighty thicker. The shop I bought the machine at doesn't carry Janome thread, she likes the other stuff better but said she would order it for me when I'm ready if that's what I want. She also said if I switch to a different bobbin thread brand, they'll adjust the bobbin tension again for me. I have unlimited classes and 2 years free service on the machine. They're really great.