Patent ID: 8151721

Claim:
A thread tensioning device for a sewing machine comprising: a limit member being fixed on the sewing machine and provided with a pulling member thereon for pulling a thread inserted through the pulling member; wherein: the limit member is provided with a rod-shaped guide portion; the pulling member is an extension coil spring, the pulling member is positioned on the guide portion and provided with an elastic extension portion which is mounted on the guide portion in such a manner that the elastic extension portion is larger in diameter than the guide portion so as to define an elastic clearance between the elastic extension portion and the guide portion when the pulling member elastic extension portion is sleeved on the guide portion, the elastic extension portion is provided with a thread pulling portion at one end thereof; the thread is pulled by the thread pulling portion in such a manner that an axial elastic deformation of the elastic extension portion is caused when the thread is pulled and the deformation provides a tension to the thread.