An electrical screwdriver capable of powering off automatically when a screw is tightened which may be operated either by a manually controlled switch or by a contact-artuation switch while the twisting force required in tightening a screw may be adjusted. When the screwdriver is pushed forward, a main shaft thereof will receive a resistance and pushes a wound end of a steel wire passing through each parts thereof and causes the other end of the wire to touch a first contact switch controlling a motor contained in the handle of the screwdriver, and thereby causes the main shaft to rotate. When the screw is tightened, the rotation head of the screwdriver will push the clutch forward and causes two spring plates in the handle to recover their downward inclined position and separate from a second contact switch controlling the supply of power. An adjusting sleeve and two adjusting screws may be used to set the screwdriver to a manually controlled operation mode by fixing the adjusting sleeve to a position near the back side. A rotation collar and a slidable member with scales indicating torsion value, together with a compression spring between them may control and decide the twisting force required in tightening a screw.

A torque limiting power screwdriver includes a housing in which there is supported for rotation and axial displacement a screwdriver spindle. A transmission transmits power from a motor to the screwdriver spindle. A torque overload coupling and a separating coupling are interposed in the transmission, being operative for interrupting the transmission of torque from the motor to the screwdriver spindle. The separating coupling is coupled and uncoupled in response to axial displacement of the screwdriver spindle between its coupling and uncoupling positions. The axial movement of the spindle is accomplished by a trigger movably mounted on the housing and connected by a Bowden cable or a lever transmission to the spindle. The spindle is connected by an axially movable coupling with an output member, especially with a bevel gear transmission accommodated in an angular head housing portion. A switching trigger is used to energize and de-energize the motor. The trigger and the switching trigger can be combined into a trigger unit, thus making possible one-hand operation. The trigger and switching trigger are so constructed and arranged that they force the succession of energization of the motor and coupling of the separating coupling during the commencement of operation, and the succession of uncoupling the separating coupling and de-energization of the motor during the termination of operation.

An angle type power nutrunner having a housing (10) with a rotation motor, an angle head (15) with an output shaft (13), and a thread connection (21) including a lock nut (22) for securing the angle head (15) to the housing (10). The housing (10) is provided with a first group of radial holes (25) disposed in a circumferentially directed row and the angle head (15) is provided with a second group of radial holes (26) disposed in a circumferentially directed row, and a key pin is arranged to positively define alternative angular positions between the angle head (15) and the housing (10) by engaging selectively one hole each of the first and second groups of holes. The pitch of the first group of holes (25) is different than the pitch of the second group of holes (26) for enabling a small angle adjustment of the angle head (15) in relation to the housing (10).