Abstract: A unitary double-acting piston thread cutter assembly having a housing including an integrated cutter section and drive section forming a single unitary device. The thread cutter assembly includes a universal tension mount for releasably securing the thread cutter assembly to the top plate of a variety of different types and models of sewing machine. A V-shaped moveable blade has two sides with a pivot point defined at the intersection of the sides. Along one side of the moveable blade is disposed a cutting or knife edge. A double-acting piston and drive link are disposed longitudinally in the housing and connected so that they are both displaced at the same time.