a self - tightening chuck mechanism is disclosed . the chuck mechanism has a jaw mechanism with a jaw elements which are slidably disposed within corresponding channels defined in a rotatable body . a threaded socket member , which is configured to be rotated in first or second directions relative to the jaw elements is rotatably disposed about and engaged with the jaw elements . an impact assembly is configured to interface with the threaded body to apply anti - rotational forces to the socket member to prevent rotation of the socket member to close the jaws when rotated in a first direction and open the jaws when rotated in a second direction . the thrust bearing is configured to apply a first set of forces to socket member when the socket member is relatively rotated in the first direction and a second set of forces when the socket member is rotated in a second direction .