The Reversible, Snap-On, Studio Follow-Focus is meant for the more robust, 15x100mm or 19x 104mm studio support rods systems
The position of the Follow-Focus in relation to the lens is adjustable and locks onto the rails with the red thumbscrew between the rail clamps. The side thumbscrew locks the Follow-Focus to the rails and allow for quick release and mounting. The control and gear box can be mounted to either side allowing for the focus-puller to work from either side of the camera.
The Petroff Follow-Focus is compact and precise without the unwanted play of competitively priced systems.