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.