Patent ID: 7430973

Claim:
A thread tension mechanism comprising: a thread tension dial that adjusts thread tension applied to a needle thread; a pair of thread tension discs allowing adjustment of thread tension applied to the needle thread by operation of the thread tension dial; a dial shaft secured unrotatably to an element constituting a body of the thread tension mechanism and rotatably supporting the thread tension dial; a first coil spring mounted in intimate contact with an outer periphery of the dial shaft; a second coil spring mounted in intimate contact with the outer periphery of the dial shaft in a position spaced from the first coil spring and being wound in a same direction as the first coil spring; and a pair of non-confronting outer end portions positioned at both ends of the first coil spring and the second coil spring or a pair of inner end portions positioned at confronting ends of the first coil spring and the second coil spring are engaged with the thread tension dial so as to be unrotatable relative to the thread tension dial.