The reversed screw (vite retrosa) and a self-moving cart
A double-handed screw taking two nuts, and a wheeled cart with rudder circling along line f g
The sheet defines the 'reversed screw' (vite retrosa): a screw whose threads begin at its middle and run in opposite hands toward the two ends, so that it takes two nuts, here marked with loads of 100 and 100 against 200. Leonardo notes that turning it drives its two nuts in contrary directions, that fixing one nut doubles the travel and effort of the other, and states the general maxim that a moving power exerts more force where it is anchored than on the thing it moves. At the foot a small wheeled cart fitted with a rudder (timone) is drawn and captioned to move in a circular path along the line f g.
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The reversed screw with threads meeting at its middle
A reversed screw is one whose turns begin at the middle of its length, depart equally from that middle, and end at the opposite extremities. It is allowed two nuts, because it is two screws of two natures joined together; turning it with contrary motions drives the two nuts along different and opposite paths.
Fixing one nut doubles the other nut's travel and effort
If, in turning the reversed screw, you stop one of its two nuts, the motion of the other nut is doubled from the first, both in length of travel and in effort.
A power exerts more force where it bears than on the load
Leonardo closes the passage with a general maxim: every power that moves exerts more force in the place where it bears, or is anchored, than in the thing moved by it.
Wheeled cart with rudder circling along line f g
The small wheeled carriage at the lower right, fitted with a rudder (timone), is captioned to move by circular motion along the line f g. Points f and g mark the axis of that circular path.