Abstract: A power tool, such as a hammer driver-drill (1), includes: a motor (8); a motor housing (7A) that holds the motor (8); a grip housing (7B) connected to the motor housing (7A); a battery mount housing or enlarged-part housing (7C) connected to the grip housing (7B); and a dial (24) that is provided in the enlarged-part housing (7C) such that it is rotatable about a dial shaft (29). A threshold for stopping the motor (8) is settable by rotating the dial (24).

Abstract: A torque wrench assembly comprises a torque wrench and a reaction arm and locking means for locking together the torque wrench and the reaction arm. The locking means comprises a connection member located on the torque wrench; an opening on the reaction arm for receipt of the connection member of the torque wrench; a locking member slidably mounted in a channel on the reaction arm, the locking member including an aperture sized to allow the connection member to pass therethrough; and biasing means arranged to bias the locking member into a position wherein the aperture is partially aligned with the opening. The connection member has an insertion end for insertion into the opening of the reaction arm, and immediately adjacent the insertion end is a recess. The recess is shaped to receive a part of the locking member.

Abstract: A tightening device and a tightening method are able to check that a fastening member has been fastened to a desired set torque or greater after being tightened, without loosening the fastening member.

Abstract: A system and method for automating an assembly process of threading a tube-nut onto a threaded connector. The system includes a robot having a force sensor and a tube-nut runner tool coupled to the robot and having a tool head with a rotatable socket therein. The method includes engaging the socket to the tube-nut under force control using the force signal from the force sensor. The tool controller causes the socket to rotate the tube-nut where the tool controller controls the torque and/or angle displacement of the tool head to tighten the tube-nut on the threaded connector. The method also includes disengaging the tool head from the tube-nut after the tube-nut is properly tightened onto the threaded connector under force control to ensure that the end member is properly disengaged from the tube-nut.

Abstract: Various torque-limiting screwdrivers, systems, and methods are disclosed. The screwdriver can include a body supporting a motor configured to rotate a screw engaged with the screwdriver. The screwdriver can include a controller configured to implement torque-limiting functionality, such as by monitoring the amount of torque applied to the screw and reducing or stopping rotation of the screw when certain torque-limiting criteria are met. Some embodiments include a threshold point, after which the torque-limiting functionality can be engaged. Some embodiments include a slowdown point, after which the rotational speed of the screw is reduced.

Abstract: A torsion assembly includes a torsion tool and at least one wireless displayer for simultaneously receiving and displaying the torsion datum from the torsion tool. The torsion tool includes a seat disposed therein and a display module detachably received in the seat. The wireless displayer includes a base and a body rotatably mounted on the base. The base can be put on a desktop or adhered on a machine by a magnet. The body can wirelessly receive and shown the torsion datum from the first wireless transceiver that is disposed in the seat on the torsion tool.

Abstract: A lock state occurrence determination apparatus includes a counter, a reset device, a reference time changing device, a lock state determination device, and an invalidation device. The invalidation device performs, in a case where a false determination of occurrence of a lock state of a motor is caused by the lock state determination device due to an operation input to operate a rotation speed of the motor, at least one of a first invalidation operation to invalidate the lock state determination device and a second invalidation operation to invalidate continuation of a counting operation by the counter.

Abstract: A tongs system and method for making and breaking threaded joints of a string of tubing for an oil well involves, in some examples, the use of a set of tongs with a two-speed transmission and a hydraulic system selectively operable in a high-pressure mode and a low-pressure mode. During an initial tightening period, the tongs system operates in high-gear and high-pressure for maximum speed. During a subsequent final tightening period, the tongs system operates in low-gear and low-pressure to controllably tighten the joint to a predetermined target torque. In some examples, to allow the transmission to shift speed without jamming gears, the tongs system pauses for an instant between the initial and final tightening periods. In some examples, the tongs system is interlocked with a hoist and/or other tube-holding and handling equipment.

Abstract: The invention describes a hand-held power tool having a drive train, which includes a motor with a rotor, a drive shaft, and a transmission. According to the invention, at least one flywheel mass is provided that is positionable rotationally symmetrical to the drive shaft and connectable to the drive shaft for co-rotation therewith.

Abstract: An electronic torque wrench a wrench head unit adapted to engage and turn a fastener, a tubular first wrench body securely engaged with the wrench head unit, a tubular second wrench body coupled and aligned with the first wrench body by a fitting member to permit rotation of the second wrench body relative to the first wrench body, a mounting shell sleeved on the second wrench body for mounting a display unit to provide a display representing a measured torque. By rotation of the second wrench body, the display unit can be adjusted to a desired angular position for being viewed easily by the user.

Abstract: A fastening system that comprises a fastener and a single tool that provides both snugging torque and final tensioning to the fastener assembly, from a single side, with a single operator, with no torque feedback. The fastener comprises a nut and a bolt with a head and a shank extending axially from the head. The shank has at least one threaded portion and at least one splined portion, the splined portion defining the end of the bolt. The splined portion remains connected to the threaded portion after final tensioning. The tool comprises a first socket and a second socket, wherein the first socket is engaged with an outer surface of the nut and the second socket is engaged with the splined portion on the fastener. Snugging torque and final tension are both controlled by the tool.

Abstract: An improved multi-bolt and nut torque wrench for installing and removing bolts or nuts from flanged joints or the like which includes a plurality of torque stations having a plurality of high torque wrenches for engaging the heads of the bolts or nuts during a high torque phase of removal or installation; a plurality of low-torque motors operatively engaged with the wrenches for rotating the bolts or nuts during the low torque phase of removal or installation; a source of hydraulic fluid for driving the low-torque motors during the low-torque phase, and driving the high-torque wrenches during the high torque phase; and a mechanism for switching between the two phases depending on the torque needed.

Abstract: A torque-regulated, manual drive, hydraulic wrench for tightening and loosening which doesn't require any outer element for operating, whether hydraulic pumps with respective supply hoses, control gauges, or hydraulic centers. The torque selection/regulation is performed by a circular slide rule mechanism.

Abstract: A single-shaft yaw electric bolt-tightening machine, comprising a base (1), a bracket (2), an electric tightening shaft assembly (14), a sleeve (15), a reaction force supporting board (16), a dedicated sleeve (17), a reaction force sleeve (18), a servomotor (19), a torque sensor (20), an angle sensor (21) and a connecting shaft (22). The bracket (2) is fixed on the base (1) and is provided with a rotary servomotor (3) and an encoder (4). The rotary servomotor (3) is connected with an output shaft (5) which is provided with a small pulley (6). The small pulley (6) is fitted with a big pulley (8) by a toothed belt (7). The big pulley (8) is connected with a rotating shaft (9). A guide rod (12) is connected with a rotating arm (10) by a shaft sleeve (11) and is fixed on a cover-plate bracket (13) in which the electric tightening shaft assembly (14) is fixed.

Abstract: An improved multi-bolt and nut torque wrench for installing and removing bolts or nuts from flanged joints or the like which includes a plurality of torque stations having a plurality of high torque wrenches for engaging the heads of the bolts or nuts during a high torque phase of removal or installation; a plurality of low-torque motors operatively engaged with the wrenches for rotating the bolts or nuts during the low torque phase of removal or installation; a source of hydraulic fluid for driving the low-torque motors during the low-torque phase, and driving the high-torque wrenches during the high torque phase; and a mechanism for switching between the two phases depending on the torque needed.

Abstract: A power tool includes an electric motor including a rotor and a stator, a torque sensor for measuring the torque value during tightening of rotatable fastening elements, and an operation control unit, integrated in or in communication with the power tool. The power tool has a device for preventing rotation of the rotor. A method for tightening rotatable fastening elements by use of the power tool is also disclosed.

Abstract: A power wrench includes a housing divided into two parts which are rotatable relative to each other: a first part including a handle and a transverse section lodging a rotation motor, and a second part including a reduction gearing, an output shaft and a rigidly attached and laterally extending reaction bar. A swivel connection is provided between the housing parts and includes an angle sensor arranged to generate signals in response to relative angular movements between the housing parts, and a power control unit communicates with the angle sensor and is arranged to at least substantially reduce the motor power as a pre-set maximum angular movement between the housing parts is exceeded as the motor is started.

Abstract: A power tool includes a motor, a first device and a second device. The motor receives a supply of an electric power from a power source externally of the power tool. The first device determines if the electric power supplied from the power source is an AC power or a DC power. The second device permits or interrupts the supply of the electric power to the motor depending on the determination of the first device.

Abstract: Power tools are taught that may include, for example, a detector for detecting impact sounds generated, e.g. by a hammer strikes an anvil or by oil pulse from an oil unit. The detector may include a receiver (30) adapted to selectively convert sound within a narrow frequency range into electric signals. Preferably, the impact sounds fall within the narrow frequency range of the receiver (30). A processor 38 may be utilized to control the motor (22) in order to stop the rotation of the hammer when a pre-determined number of impact sounds has been detected by the detector. In addition or in the alternative, various structures can be used to set various operating conditions, including dials 34, sound sensors 30, keypads and remote control devices 250. Further, structures for performing maintenance condition status checks are taught.

Abstract: The invention relates to a power screwdriver (10) comprising a motor (12) and a control circuit (22) which switches the motor (12) off by means of a switch-off signal (s_Stop) when it reaches a preset desired torque value (Md_Soll), and a supporting arm (18) which absorbs energy during screwing. The invention is characterized by a voltage limiting circuit (46) that limits the motor voltage (u_Mot) occurring on the motor (12) when the energy stored in the supporting arm (18) of the motor (12), which is driven as the generator and rotates counter to the direction of drive, is dissipated, to a predetermined limiting voltage (u_Lim). The limiting voltage (u_Lim) is fixed in such a manner that the motor (12) is capable of rotating without counter-torque counter to the direction of drive when operated in the generator mode and that yet no inadmissible overvoltages occur.

Abstract: An improved multi-bolt and nut torque wrench for installing and removing bolts or nuts from flanged joints or the like which includes a plurality of torque stations having a plurality of high torque wrenches for engaging the heads of the bolts or nuts during a high torque phase of removal or installation; a plurality of low-torque motors operatively engaged with the wrenches for rotating the bolts or nuts during the low torque phase of removal or installation; a source of hydraulic fluid for driving the low-torque motors during the low-torque phase, and driving the high-torque wrenches during the high torque phase; and a mechanism for switching between the two phases depending on the torque needed.

Abstract: The present invention relates to a digital power torque wrench of indirect transmission, which is composed of an eccentric driving module, a sensing module, a ratchet module and a control module. The eccentric driving module is used for transmitting power to the sensing module and the ratchet module for driving the ratchet module rotate accordingly and thus transferring the momentum of the rotating to fasten a workpiece, such as a bolt or nut. The sensing module is capable of detecting the deformation of the ratchet module as it is rotating against an increasing resistance during the fastening process, and converting the detected deformation into a signal to be received by the control module. The control module is capable of quantifying the signal for converting the same into a numerical signal representing a torque detected by the sensing module and then sending the numerical signal to a display device for displaying.

Abstract: An improved multi-bolt and nut torque wrench for installing and removing bolts or nuts from flanged joints or the like which includes a plurality of torque stations having a plurality of high torque wrenches for engaging the heads of the bolts or nuts during a high torque phase of removal or installation; a plurality of low-torque motors operatively engaged with the wrenches for rotating the bolts or nuts during the low torque phase of removal or installation; a source of hydraulic fluid for driving the low-torque motors during the low-torque phase, and driving the high-torque wrenches during the high torque phase; and a mechanism for switching between the two phases depending on the torque needed.

Abstract: Power tools are taught that may include, for example, means for detecting impact sounds generated, e.g. by a hammer strikes an anvil or by oil pulse from an oil unit. The detecting means may include a receiver (30) adapted to selectively convert sound within a narrow frequency range into electric signals. Preferably, the impact sounds fall within the narrow frequency range of the receiver (30). A processor 38 may be utilized to control the motor (22) in order to stop the rotation of the hammer when a pre-determined number of impact sounds has been detected by the detecting means. In addition or in the alternative, various means for setting various operating conditions are taught, including dials 34, sound sensors 30, keypads and remote control devices 250. Further, means for performing maintenance condition status checks are taught.

Abstract: A rechargeable motor-driven ratchet wrench having power-off protection of the present invention includes a motor, a rechargeable battery and a power-off protection device. When the loaded current of the motor exceeds a set default value of a reference circuit, the power-off protection device disconnects the power supply of the rechargeable battery, so as to stop the motor operation. With the circuit design of the power-off protection device, the ratchet wrench can be ensured to provide usage safety and also usage lifespan of the ratchet wrench can be extended.

Abstract: Disclosed is a method for screwing in and tightening a screw connection (1) to a predetermined tightened level (2), especially a predetermined torque level (2) or a predetermined pretension level, with the aid of a hand-held screwing tool (3) comprising a regulated drive unit (4) and/or control functionality, particularly an electric nut runner (3). A tightening phase (B-C-D), during which the screw head rests against the supporting surface (6) of the screw connection (1), starts following a screwing phase (A). In order to improve said method, the speed (N) of the screwing tool (3) is increased to an output speed (7) for the tightening phase (B-C-D) within an acceleration time (8) in the tightening phase (B-C-D) and is lowered within a delay time (9) prior to or until reaching the predetermined tightened level (2).

Abstract: A tightening tool for tightening a fastener is disclosed which comprises a motor and a main shaft that engages with the fastener. A clutch is disposed between the motor and the main shaft so that the clutch rotates the main shaft by transmitting torque from the motor to the main shaft when a load acting on the main shaft is less than a predetermined value. The clutch shuts off torque transmission from the motor to the main shaft when the load acting on the main shaft reaches or exceeds the predetermined value. When in use, the current flowing to the motor and rotation angle of the main shaft of the motor are detected. The detected current and rotation angle are used to determine whether the tightening torque of the fastener is normal.

Abstract: An electronic torque wrench for engaging a workpiece, the electronic torque wrench including a wrench body and a wrench head disposed on the wrench body, the wrench head being configured to engage the workpiece. A grip handle is disposed on the wrench body opposite the wrench head and a user interface is carried by the wrench body. The user interface includes a digital display with a first readout and a second readout, and an input device for inputting a preset torque value. The first readout displays a peak torque value continuously during operations and the second readout displays an applied torque value continuously during operations.

Abstract: A novel impact wrench is provided herein, which allows a user to set a target torque level, show the torque level in a display, and automatically stops the motor when the target torque level is reached. The impact wrench is constructed such that its electrical current would be at a maximum when it engages an impact operation, and at a minimum after the impact operation. The electrical current exhibits a periodic pulse and the periodic pulse is used to calculate the number of times of impacts. The torque level of the impact wrench could then be determined by the number of times of impacts.

Abstract: The present invention relates to a digital power torque wrench of indirect transmission, which is composed of an eccentric driving module, a sensing module, a ratchet module and a control module. The eccentric driving module is used for transmitting power to the sensing module and the ratchet module for driving the ratchet module rotate accordingly and thus transferring the momentum of the rotating to fasten a workpiece, such as a bolt or nut. The sensing module is capable of detecting the deformation of the ratchet module as it is rotating against an increasing resistance during the fastening process, and converting the detected deformation into a signal to be received by the control module. The control module is capable of quantifying the signal for converting the same into a numerical signal representing a torque detected by the sensing module and then sending the numerical signal to a display device for displaying.

Abstract: A hand held instrument for carrying out some function on a work piece. The instrument is a handpiece that is held by the user and includes a working element at the distal end of the handpiece for working on the work piece. There is a source of power that activates the working element by providing power thereto in various forms. There is also a pressure sensor that senses the pressure between the working element and the handpiece. In one embodiment that pressure sensor senses a predetermined pressure in order to couple the power source to the working element for activating the working element. In another embodiment, the pressure sensor senses a reduction in pressure between the working element and the handpiece to illuminate an indicator light.

Abstract: An object is to improve accuracy of tightening torque and to shorten time necessary for fastening a screw in an impact type screw fastening device that uses an electric motor as a rotation driving source. A control method for the impact type screw fastening device that uses an electric motor as a rotation driving source includes the steps of driving the motor to rotate by supplying current to the motor intermittently so that torque exerted on a load by rotation of the motor becomes like pulses on the time axis, and controlling the current of every time of each pulse so that an increment of every time of each pulse of the torque after the torque reaches a target approach torque TQN that is a first set value becomes smaller than that before it reaches the target approach torque TQN.

Abstract: The present invention relates to a power-wrench comprising an electrical converter-fed motor having a permanent-magnetized rotor and a stator provided with winding, the motor winding (1) comprising at least two winding parts, which independently of each other are connected and disconnected by a switch-over device (4). According to the invention, a first winding part (2) may be arranged to control the magnetic field of the motor so that the motor, having the first winding part (2) connected, is adapted for the threading-down phase of the nut driving and operates with low torque and high number of revolutions adapted to said phase, as well as that a second winding part (3) may be arranged to control the magnetic field of the motor so that the motor, having the second winding part (3) connected, is adapted for the final-threading phase of the nut driving and operates with high torque and low number of revolutions adapted to said phase.

Abstract: A power tool generally includes a housing and a motor assembly connected to a transmission assembly. The motor assembly and the transmission assembly are secured against rotation in the housing. A plurality of protrusions extends from a component of the transmission assembly. The power tool further includes an output spindle and a spindle lock assembly that connects the output spindle to the transmission assembly. The spindle lock assembly includes an anvil, an outer ring member and a plurality of roller members. The roller members and the protrusions are disposed between the anvil and the outer ring member. An indicator member extends from the outer ring member. A compliant member connects the outer ring member to an interior portion of the housing. A scale is connected to an exterior portion of the housing, wherein the indicator member moves relative to the scale to indicate a value of torque at the output spindle.

Abstract: An electric screwdriver capable of reducing the reactive force produced on the occasion of a screw tightening work, etc. The electric screwdriver is designed to transmit the rotational driving force of a first motor to the bit through a bit holder, and it includes a flywheel rotatively driven by a second motor in the direction same as the direction of rotation of the bit holder, a brake generating a reactive force in the direction offsetting the reactive force transmitted from the bit to the body casing through the bit holder, by braking the flywheel, and a brake operating mechanism for operating the brake in response to the magnitude of the reactive force transmitted from the bit to the body casing through the bit holder.

Abstract: Disclosed herein is a variable speed tool useful for use with securing or removing industrial fasteners. The tool also includes a means to torque the fastener to a certain precise torque. The tool can be used with an associated controller that provides control commands to the tool.

Abstract: In accordance with one embodiment of the present invention, a driver may include an electric motor coupled to a bit interface. The bit interface may include a generally cylindrical body having first and second hollow portions. The first hollow portion may be on one end of the generally cylindrical body and may define a generally cylindrical hole. The second hollow portion may abut the first hollow portion and define an oblong channel. The oblong channel may be further defined by first and second parallel flat walls. The cylindrical body may also include a first transverse groove.

Abstract: Disclosed herein is a variable speed tool useful for use with securing or removing industrial fasteners. The tool also includes a means to torque the fastener to a certain precise torque. The tool can be used with an associated controller that provides control commands to the tool.

Abstract: A torque-angle wrench has a torque preset alert circuit which provides a first signal when a predetermined torque level is reached, an angle sensing circuitry providing a second signal corresponding to angular rotation, output circuitry responsive to the second signal for providing an indication of angular rotation, and switch circuitry for preventing the second signal from reaching the output circuitry until the occurrence of the first signal.

Abstract: This dynamic calibration qualifier relates to a tool monitor and assembly qualifier that verifies that the correct number of fasteners have been properly installed into an assembly. The device monitors an analog signature created by the tool and has the ability to dynamically calibrate itself while the tool is running. In the preferred embodiment, the stored variable is a clutch offset identified during a calibration phase. In a pulse tool, the programmed microprocessor is configured to identify and store the peak pressure of the first three pulses which are averaged together. The clutch offset is added to the average pulse value from which the clutch threshold is generated.

Abstract: The device for screwing on a cap comprises a gripping head fixed to a rotary spindle, and a drive shaft connected to a drive member carried by a frame, the rotary spindle and the drive shaft are connected to each other on the same axis by a resilient coupling member, connected both to the rotary spindle and to the drive shaft, and the device further comprises a detector member for detecting relative rotation between the rotary spindle and the drive shaft, and a control member for interrupting tightening of the cap when the relative rotation reaches a predetermined threshold.

Abstract: A power tool such as an electric drill typically contains a gear train that couples the output spindle of the motor to the tool bit-receiving chuck. The control circuit for the power tool is operable in a ratcheting or pulse mode that causes the output spindle to rotate in discrete incremental amounts. Corresponding methods for controlling the operation of the electric motor of a power tool are also disclosed.

Abstract: A torque tool assembly having an elongated unitary, cylindrical main housing and including a drive motor subassembly and a gear train subassembly coaxially supported and operatively connected in the cylindrical housing and held in operative engagement by a resilient spring structure while being mechanically, removably locked together in the main housing whereby loosening and/or mis-aligning of the operative connection between the drive motor subassembly and gear train subassembly from vibration and other loads is substantially precluded.

Abstract: A screw driving power tool including a housing (1, 31), a handle (2, 32) connected with the housing (1, 31), an actuation switch (3, 33), a screw driving device (18, 48) for receiving a screw-containing magazine (21, 51) and releasably connected with the housing (1, 31), an electric motor (5, 35) located in the housing (1, 31) and having a drive shaft (6, 36); an operating spindle (7, 37) operatively connected with the drive shaft (6, 36) of the electric motor (5, 35), a screw driving working tool (11, 41) for driving screws and connected with the operating spindle (7, 37), and an adjustable torque cut-off device for cutting a torque transmittable to the operating spindle off.

Abstract: A power tool system comprises a portable power tool (10), an operation control device (11) including an integrated memory (16) for storing power tool operation data, and an auxiliary memory module (18) normally containing the same power tool operation data as the integrated memory (16) easily connectable and disconnectable in relation to the control the operation control device (11), wherein the auxiliary memory module (18) serves as a removable back-up memory intended to carry operation data from one operation control device to another, notwithstanding the control device being integrated part of a battery powered tool or a separate unit at a main powered tool.

Abstract: A fastening apparatus 10 for tightening a threaded fastener 14 into a component, the apparatus comprising a drive mechanism 12 for rotating the threaded fastener and a detector for detecting a transitional tightening stage when tightening the threaded fastener to the component, wherein the apparatus operably applies a first set of tightening conditions to the threaded fastener during a first tightening stage, and a second set of tightening conditions during a second tightening stage in response to the detection of the transitional tightening stage by the detector.

Abstract: A tube spinner for assembling vehicle tie rod assemblies is disclosed. The tube spinner includes a support structure for supporting a tapped tube, a rotating device for rotating the tube within the support structure into threaded engagement with one or more sockets simultaneously and a restraining structure for locking the sockets against rotation. In a preferred embodiment, a plurality of casters are provided for supporting a tube along a main axis of the tube. Generally U-shaped tracks are placed adjacent left and right ends of the tube to prevent rotation of sockets being attached to the left and right ends of the tube. A motor driven friction wheel is brought into engagement with an outer circumference of the tube for rotating the tube along its main axis and simultaneously threading the tube onto one or more sockets.

Abstract: A screw setting tool including a housing (1), a tool spindle (8) located in the housing (1) and axially displaceable relative thereto, a bit stop (2) provided in the housing (1) for limiting an axial displacement of the tool spindle (8) in a direction opposite to the screw-in direction and adjustable in a direction parallel to a screw-in direction, a spring (10) for biasing the tool spindle (8) in the screw-in direction, and a torque clutch (3) for connecting the tool spindle (8) with a drive motor, the torque clutch (3) having a first clutch member (4) driven by the drive motor, a second clutch member (6) fixedly connectable with the tool spindle (8) for joint rotation therewith, and an intermediate clutch member (5) located between the first and second clutch members (4, 6) and supported on the tool spindle (8) for rotation therearound and an axial displacement relative thereto between an entraining position, in which the intermediate clutch member (5) transmits torque from the first clutch member (4) to th

Abstract: A device for tightening a plurality of threaded members at the same time with proper torque without necessitating a cumbersome procedure of rotating the members one by one through a specified small angle at a time and without unequivalent tightening of the members, the tightening device (1) comprises two rotary shafts (6) each provided at a forward end thereof with a wrench portion (8) fittable to the threaded member (44), motors (3) for individually driving the rotary shafts (6) and a control unit (9) for detecting the tightening torque of each threaded member (44) and controlling the motor (3) based on the detected value to ensure proper tightening, the control unit (9) checking the tightening torque of each threaded member (44) as to whether the torque is within a predetermined range and whether the difference in tightening torque between the threaded members (44) is within a predetermined range.

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.