Movable Spring Feed-Duct 31 March 2017, 19:00 Sorry, your browser doesn't support embedded videos, but don't worry, you can download it and watch it with your favorite video player! A close-wound spring attached to a hopper is used as a movable feed-duct for balls or short rollers. « previous mechanism Inverse Parallelogram Mechanism next mechanism » Lever of Stable Neutral Position load comments Please enable JavaScript to view the comments.