A reversible power wrench comprises a housing (10), a rotation motor, and a power transmission coupling the motor to an output shaft (21), including a reduction gearing (20) with first planetary gearing (28) for transferring torque in the "forward" direction of rotation and a second planetary gearing (29) for transferring torque in the "reverse" direction of rotation. The first and second planetary gearings (28, 29) have rotationally interconnected sun gears (31, 39) and a common planet wheel carrier (34). The second planetary gearing (29) comprises an inner set of planet wheels (37) intermeshing with the sun gear (39) and an outer set of planet wheels (38) intermeshing with the inner set of planet wheels (37) and engageable with a ring gear (40) which is axially shiftable between an "forward" position in which it engages the planet wheels (33) of the first planetary gearing (28) only and a "reverse" position in which it engages the outer sets of planet wheels (38) of the second planetary gearing (29) only. Speed responsive centrifugal weights (46) prevent by positive locking the ring gear (40) from being shifted during operation of the power wrench. IMAGE
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