Abstract: A prismatic (18) having a square cross-section is provided in a rotation shaft (16) to which plug terminals (14) are fixed. The rotation shaft (16) is sandwiched between a pair of elastic pieces (17a), (17a) of an elastic holder (17), so that the respective elastic pieces (17a), (17a) are brought into contact with plane surfaces of the prismatic bar (18) parallel to each other. Therefore, an interval between the two elastic pieces (17a), (17a) of the elastic holder (17) is increased when the square bar (18) rotates, so that a firm and steady touch of a click can be provided.

Abstract: A prismatic bar 18 having a square cross-section is provided in a rotation shaft 16 to which plug terminals 14 are fixed, and the rotation shaft 16 is sandwiched between a pair of elastic pieces 17a, 17a of an elastic holder 17, so that the respective elastic pieces 17a, 17a are brought into contact with plane surfaces of the prismatic bar 18 parallel to each other. Therefore, an interval between the two elastic pieces 17a, 17a of the elastic holder 17 is increased when the square bar 18 rotates, and thus, a firm and steady touch of a click can be provided.

Abstract: A reduction gear mechanism, incorporating a speed changing mechanism, for use with a motor-driven drill. The mechanism includes at least one planetary speed reducer having a sun gear to which rotation of an electric motor is transmitted, a plurality of planet gears arranged around the sun gear and engaged with the sun gear, an internal gear internally engaged with the planet gears, and a planet gear holding plate which pivotally supports the planet gears on one side of it and has an output shaft on the other side of it. The internal gear of at least one planetary speed reducer includes a cylindrical internal gear. The reduction gear includes mechanisms for locking the cylindrical internal gear to prevent rotation of the cylindrical internal gear and for engaging the cylindrical internal gear with the planet gear holding plate so that the cylindrical internal gear and the planet gear holding plate rotate as a single unit.