Thread tension device for a sewing machine

A thread tension device for a sewing machine comprising a plate engaged on said sewing machine, a bolt including a first end rotatably engaged in said plate and a second end extended outward of said sewing machine, a stop formed on said plate and extended inwards of said sewing machine, a limiting means engaged on said first end of said bolt for engagement with said stop in order to limit said bolt to rotate for one turn, a pin engaged on said plate and extended outwards of said sewing machine, a knob fixed on said second end of said bolt, a dial rotatably engaged on said bolt and including at least one hole formed therein for engagement with said pin of said plate and including at least one lever extended away from said plate, a pair of discs engaged between said plate and said dial and engaged on said bolt for clamping a thread, a follower threadedly engaged on said bolt and including at least one notch formed therein for engagement with said lever of said dial such that said follower is prevented from rotating relative to said dial and is guided to move longitudinally along said lever, and biasing means biased between said dial and said follower for biasing said discs together, whereby, said follower is rotatable by said dial when said dial is pushed inwards of said knob and when said pin is disengaged from said hole of said dial.