This single-sided follow focus has a 1:1 hand wheel-to-gear ratio for extremely accurate focus pulls. It attaches to both 15mm LWS and 19mm rod supports by snapping onto the rods. This allows you to adjust, mount and remove it without the need to remove other accessories that are also mounted onto the rods (such as matte boxes and lens supports). The gear is attached to a swivel that allows you to rotate it against the lens for a tight fit. You can also slide the whole unit from side-to-side, allowing you to easily adjust to fit any size of lens.