A rotary indexing mechanism for indexing a shaft or shaft mounted member in precise rotary increments and with precise end-of-movement positioning includes a reciprocable rack and pinion mechanism coupled to a rotatably mounted shaft. The pinion is coupled to the shaft through a one-way clutch so that movement of the rack in a first direction is coupled through the clutch to cause a corresponding rotation of the shaft with the clutch uncoupling the shaft during movement of the rack in the opposite direction. A first stop member(s) is carried by the shaft for movement along a path that orbits the shaft axis. A second stop member is carried by the rack along a linear path that intersects the orbit of the first stop member. As the rack rotates the shaft through a rotary increment, the rack-carried second member is positioned in the orbit of the first stop member with the two members engaging to halt further rotary movement. The rotary indexing mechanism allows successive rotary increments with precise end-of-movement positioning determined by the two interengaging members. In the preferred embodiment, one or both of the members is adjustable to provide various end-of-movement positions.