Abstract: A clutch mechanism includes a first clutch plate retaining circular columnar engagement members and a second clutch plate retaining spherical engagement members. In the second clutch plate, inner retaining holes and outer retaining holes positioned more radially outward than the inner retaining holes are formed. The outer retaining holes are larger in diameter than the inner retaining holes. On assembly of the clutch mechanism, engagement members are selected from small-diameter spherical engagement members corresponding to the small-diameter inner retaining holes and large-diameter spherical engagement members corresponding to the large-diameter inner retaining holes. The selected engagement members are disposed in the corresponding retaining holes, respectively. The maximum rotational torque is greater when the large-diameter spherical engagement members are selectively disposed than when the small-diameter spherical engagement members are selectively disposed.

Abstract: A clutch mechanism includes a first clutch plate retaining circular columnar engagement members and a second clutch plate retaining spherical engagement members. In the second clutch plate, inner retaining holes and outer retaining holes positioned more radially outward than the inner retaining holes are formed. The outer retaining holes are larger in diameter than the inner retaining holes. On assembly of the clutch mechanism, engagement members are selected from small-diameter spherical engagement members corresponding to the small-diameter inner retaining holes and large-diameter spherical engagement members corresponding to the large-diameter inner retaining holes. The selected engagement members are disposed in the corresponding retaining holes, respectively. The maximum rotational torque is greater when the large-diameter spherical engagement members are selectively disposed than when the small-diameter spherical engagement members are selectively disposed.

Abstract: A power tool including a drive, and a planetary gear speed reducer reducing the speed of rotation transmitted from the drive. The planetary gear speed reducer has a positioning ball between a first sun gear and a second sun gear. The first sun gear has an annular engagement portion smaller in diameter than the positioning ball, and the second sun gear has a ball-retaining recess accommodating at least half of the positioning ball and retaining the positioning ball at a position on a rotation axis of the second sun gear. The ball-retaining recess has a bottom surface substantially perpendicular to the rotation axis and a cylindrical inner surface to retain the positioning ball at a point on the rotation axis. A gap is formed between the first sun gear and the second sun gear when the positioning ball is sandwiched between the annular engagement portion and the bottom surface.

Abstract: Provided is a threaded member tightening tool capable of returning a count value in linkage with reverse driving by the threaded member tightening tool and only when a threaded member to be removed by the reverse driving has been counted as a tightened threaded member. A computing unit of a motor-driven screwdriver is switchable between a counting mode in which the computing unit counts the number of tightened threaded members and holds the counted number as a count value and a count return mode for returning the count value to a one-preceding count value. The computing unit returns the count value to a one-preceding count value based on the fact that the engaging element fitting unit has been driven in the reverse direction when the computing unit has been switched to the count return mode.

Abstract: Provided is a threaded member tightening tool capable of returning a count value in linkage with reverse driving by the threaded member tightening tool and only when a threaded member to be removed by the reverse driving has been counted as a tightened threaded member. A computing unit of a motor-driven screwdriver is switchable between a counting mode in which the computing unit counts the number of tightened threaded members and holds the counted number as a count value and a count return mode for returning the count value to a one-preceding count value. The computing unit returns the count value to a one-preceding count value based on the fact that the engaging element fitting unit has been driven in the reverse direction when the computing unit has been switched to the count return mode.

Abstract: A power tool including a drive, and a planetary gear speed reducer reducing the speed of rotation transmitted from the drive. The planetary gear speed reducer has a positioning ball between a first sun gear and a second sun gear. The first sun gear has an annular engagement portion smaller in diameter than the positioning ball, and the second sun gear has a ball-retaining recess accommodating at least half of the positioning ball and retaining the positioning ball at a position on a rotation axis of the second sun gear. The ball-retaining recess has a bottom surface substantially perpendicular to the rotation axis and a cylindrical inner surface to retain the positioning ball at a point on the rotation axis. A gap is formed between the first sun gear and the second sun gear when the positioning ball is sandwiched between the annular engagement portion and the bottom surface.

Abstract: Provided is a motor-driven screwdriver configured such that the upper limit value of transmittable rotational driving force differs between forward and backward rotation. The motor-driven screwdriver has a bit holder and a rotational driving force transmission device for transmitting rotational driving force to the bit holder. The rotational driving force transmission device has a driving member, a driven member having through-holes, power transmission members held in the through-holes, respectively, and an urging member urging the power transmission members inward. Each through-hole is provided such that a through-hole center axis passing through a center between a forward rotation guide surface and backward rotation guide surface of the through-hole does not intersect a rotation center axis, whereby the force with which the power transmission member is pushed radially outward is made to differ between forward and backward rotation.

Abstract: A motor-driven screwdriver operation information indicator is retrofittable to a motor-driven screwdriver to indicate information related to an operation of the motor-driven screwdriver. An indicator housing of the operation information indicator is secured to a supporting and securing member configured to be secured to an outer peripheral surface of a screwdriver housing of the motor-driven screwdriver, thereby holding the indicator housing at a rear position of a rear end portion of the motor-driven screwdriver. An indication control circuit disposed in the indicator housing is connected to at least one of a motor-driven screwdriver drive control circuit and an external control circuit to receive a signal from the circuit connected thereto. The indication control circuit transmits a signal related to an operation of the motor-driven screwdriver on the basis of the received signal and indicates information related to the operation of the motor-driven screwdriver on an operation information indicating part.

Abstract: A motor-driven screwdriver accessory is externally attached to a motor-driven screwdriver body. The body has a drive control circuit disposed in a screwdriver housing, a power supply cord connected to the drive control circuit and extended through a first power supply cord holding hole, and a securing annular member secured to the outer periphery of the power supply cord. The accessory has a housing having a second power supply cord holding hole sized to allow the securing annular member to be engagingly secured thereto. The first power supply cord holding hole has a size allowing formation of a clearance between the first power supply cord holding hole and the power supply cord in a state where the power supply cord securing annular member is secured to the second power supply cord holding hole, thereby enabling a signal line from the drive control circuit to be routed through the clearance.

Abstract: A motor-driven screwdriver accessory is externally attached to a motor-driven screwdriver body. The body has a drive control circuit disposed in a screwdriver housing, a power supply cord connected to the drive control circuit and extended through a first power supply cord holding hole, and a securing annular member secured to the outer periphery of the power supply cord. The accessory has a housing having a second power supply cord holding hole sized to allow the securing annular member to be engagingly secured thereto. The first power supply cord holding hole has a size allowing formation of a clearance between the first power supply cord holding hole and the power supply cord in a state where the power supply cord securing annular member is secured to the second power supply cord holding hole, thereby enabling a signal line from the drive control circuit to be routed through the clearance.

Abstract: A motor-driven screwdriver operation information indicator is retrofittable to a motor-driven screwdriver to indicate information related to an operation of the motor-driven screwdriver. An indicator housing of the operation information indicator is secured to a supporting and securing member configured to be secured to an outer peripheral surface of a screwdriver housing of the motor-driven screwdriver, thereby holding the indicator housing at a rear position of a rear end portion of the motor-driven screwdriver. An indication control circuit disposed in the indicator housing is connected to at least one of a motor-driven screwdriver drive control circuit and an external control circuit to receive a signal from the circuit connected thereto. The indication control circuit transmits a signal related to an operation of the motor-driven screwdriver on the basis of the received signal and indicates information related to the operation of the motor-driven screwdriver on an operation information indicating part.

Abstract: Provided is a motor-driven screwdriver configured such that the upper limit value of transmittable rotational driving force differs between forward and backward rotation. The motor-driven screwdriver has a bit holder and a rotational driving force transmission device for transmitting rotational driving force to the bit holder. The rotational driving force transmission device has a driving member, a driven member having through-holes, power transmission members held in the through-holes, respectively, and an urging member urging the power transmission members inward. Each through-hole is provided such that a through-hole center axis passing through a center between a forward rotation guide surface and backward rotation guide surface of the through-hole does not intersect a rotation center axis, whereby the force with which the power transmission member is pushed radially outward is made to differ between forward and backward rotation.