Don't have an answer regarding number for tension setting, but a caution...please don't mess with bobbin tension unless you know what you're doing...most tension issues can be taken care of on newer machines by simply working the top tension. Bobbin tension is more difficult to adjust and just as difficult to return to normal. As someone suggested, make a sample sandwich and try the thread on various settings....if you don't have an instruction manual for your machine you may be able to get one on-line