Torque limiting screw-tightening tool

A power-operated tool is fitted with a drive, whose driving shaft can, by means of a connecting coupling whose actuation depends on the reaction torque, be coupled with a driven shaft. The connecting coupling first interrupts transfer of the torque to the driven shaft, so that, in spite of the running drive, no torque can be transferred to the driving shaft. Immediately afterwards, the drive is disconnected. As a result of this sequence of disconnections, the motor, which continues running, can no longer have any influence on the work in progress so that the fastener being tightened does not reach the point of plastic deformation.