Abstract: In the indexing mechanism, for producing rotary indexing of a primary sprocket or pulley, a locking bracket is operable to alternately lock or unlock the primary sprocket or pulley. At the same time, the locking bracket alternately unlocks or locks an endless chain or synchronous belt at a locking location. The chain or synchronous belt passes around the primary sprocket or pulley and past the chain or synchronous belt locking location. The chain or synchronous belt has first and second loops between the primary sprocket or pulley and the chain or synchronous belt locking location, on opposite sides thereof. First and second secondary sprockets or pulleys are mounted on the ends of first and second cylinder rods respectively, each secondary sprocket having one of the loops passing over it. The locking bracket is moved between two positions, to lock either the sprocket or pulley, or the chain or synchronous belt at the locking location.