Abstract: The assembly tool comprising an electrically operated clutch assembly and achieves rapid termination of energy throughput to provide accurate torque delivery for fastener tightening and similar applications. The clutch assembly includes a pair of equal diameter, axially aligned input and output hubs having a wrap-spring disposed thereabout. One end of the wrap-spring is coupled to the input hub and the other is coupled to a control annulus disposed concentrically and freely rotatably about the output hub. An electromagnet also concentrically disposed about the output hub is activated to couple the control annulus to the output hub. A resulting drag on the wrap-spring tightens it about the output hub and power is transmitted. Deactivation of the electromagnet provides rapid release of the wrap-spring and termination of power throughput. A one way (overrunning) clutch couples the hubs when power is applied in the opposite direction to, for example, facilitate removal of fasteners.