Abstract: A mechanism for rotating about a vertical axis generally flat-bottomed objects which are moving along the working surface of a conveyor system, the mechanism including at least three rollers which are rotatable about horizontal axes and which are oriented so as to be tangent to the circumference of a circle which is concentric with the vertical axis, a support frame for moving the rollers into an active positioning above the working surface of the conveyor system and downwardly to an inactive positioning therebelow, and a belt drive system for rotating all of the rollers in the same direction with respect to the circumference of the circle.