This is a single sided Follow Focus that can clip into 15mm rods even after your rig is built. It only fits on 60mm handheld spacing. It has a nice smooth movement, and its 43 tooth 0.8 pitch gear can be moved to either side of the gear box to accommodate spacing of other rod accessories. The focus rings on many DSLR lenses have clutch mechanisms and will keep rotating even after they reach the “end” of their travel. They need to do this in order to accommodate autofocus mechanisms for taking still photos. The problem is that many people want to use still lenses for video, and video people need repeatable focus stops at close focus and infinity. This follow focus solves that problem by letting you set artificial hard stops on a DSLR lens. The stops can be easily disengaged by lifting a collar in the handset. MidCan has geared focus rings that can be attached to DSLR lenses of different diameters.