Rotating the bevel gear with a volt wrench, the bevel gear drives the plane rectangular thread, and then drives the three-claw centripetal movement. Because the pitch of the plane rectangular thread is equal, the three-claw movement distance is equal and there is self-centering. The three-jaw chuck consists of a large bevel gear, three small bevel gears and three claws. The three small bevel gears mesh with the large bevel gears. The back of the large bevel gears has a flat thread structure, and the three claws are equally divided on the flat threads. When the small bevel gear is pulled with a wrench, the large bevel gear rotates, and the flat thread on the back side causes the three jaws to approach or exit toward the center at the same time.
The four claws are used to drive the four claws, so the common four-jaw chuck does not have the function of self-centering. However, it is possible to clamp various rectangular and irregular workpieces by adjusting the position of the four claws.