Abstract: A lens assembly includes a third lens group frame having an end face extending in an optical-axis direction provided with an end-face cam having displacement along a peripheral direction, for retaining a third group of lenses, a second lens group frame having a cam follower abutted against the end-face cam for retaining a second group of lenses, a second lens group spring for biasing the second lens group frame toward the third lens group frame, a rotational regulating for regulator rotation of one of the third lens group frame and the second lens group frame around an optical axis, and rotator for rotating the other of the third lens group frame and the second lens group frame around an optical axis when zoom operation is performed, wherein the end-face cam and a cam follower are operated by relative angular movement of the third lens group frame and the second lens group frame, around the optical axis at the time the zoom operation is performed to modify spacing therebetween in the optical-axis direction.

Abstract: An agricultural tractor transmission to which various attachments may be removably affixed as necessary. Such attachments include a super reduction device and a pump for actuating a work implement.

Abstract: Electrochemical treatment process is characterized in that said treatment is carried out by containing 2-60 v/v % of dispersed bubbles having the first quartile diameter being not more than 2,000 .mu.m in the electrolyte solution and by applying voltage.

Abstract: A clutch comprising a drive rotary member, a driven rotary member engageable with and disengageable from the drive rotary member by being moved relative thereto in the directions of axis of rotation, an annular cam interposed between the drive rotary member and the driven rotary member, and an engaging member manually operably mounted on a case to prevent rotation of the cam. When the engaging member is operated to project toward the driven rotary member through the cam, the driven rotary member is held out of engagement with the drive rotary member reliably.

Abstract: A speed change unit for a tiller comprising three shafts, two shift gears having a large width axially thereof and two driven gears, one of the driven gears being freely rotatably mounted on one of the shafts and selectively meshable with one of the shift gears and another gear being fixedly mounted on the same shaft and selectively meshable with one of the shift gears, thereby the rotation of one of the driven gears on the shaft can be delivered to a transmission system for axles via two transmission systems different in speed change ratio and same in the direction of transmission of rotation.

Abstract: A hammer is movable to strike paper against a rotatable type member through a ribbon for printing. The hammer is moved for printing by a rotary shaft formed with a projection which engages with the hammer upon rotation of the shaft. A rockable ribbon guide holds the ribbon which has upper and lower portions provided with different colors of ink. A setting lever is pivotally connected to the ribbon guide in such a manner that rocking movement of the setting lever produces rocking movement of the ribbon guide. The setting lever is formed with two engaging portions with which latch members of two solenoids are respectively engagable. A spring urges the setting lever toward a reset position. A first one of the solenoid latch members is arranged to hold the setting lever in a first set position at which one of the colors on the ribbon is in a printing position.