Abstract: A device for tightening a bolt or a nut has a tightening socket which is releasable from biting engagement with the bolt or nut by disengaging a clutch in a rotation transmission system after completion of tightening, and which is made readily removable from the bolt or nut. The device is characterized in that it comprises power transmission means for coupling a socket drive motor to the socket for power transmission, the clutch incorporated in the power transmission means for selectively effecting or interrupting power transmission from the motor to the socket by a sliding movement, and clutch control means for selectively moving the clutch to an engaged position or a disengaged position. The clutch is moved to the disengaged position by the clutch control means after the motor is deenergized, whereby residual torque delivered by the motor to the bolt or the nut is removed to preclude biting engagement of the socket with the bolt or nut.

Abstract: A bolt tightening device for tightening torque controlled bolts each having at one end thereof a tip to be sheared has an outer socket engageable with a nut, and an inner socket engageable with the tip, the inner socket being axially slidable relative to the outer socket and biased outward by a spring, the two sockets being coupled to planetary gear mechanisms for delivering opposed torques to the respective sockets, a knockout pin extending into the inner socket for forcibly removing the bolt tip as sheared. The knockout pin for knocking out the sheared bolt tip is made contractable by being composed of a shank and a head provided on the shank and biased outward of the shank by a spring, The length of backward stroke of the knockout pin required for knocking out the tip is minimized by contracting the pin to thereby shorten the length of the device.