A Giant Auger for Boring Holes in the Ground
With cutters for the earth's female thread, and a lock and key
The central study is a large earth auger — a great screw mounted on a tripod frame and turned like an auger to sink a pit up to a braccio and a half deep. Once driven in twice its own length, a trestle and handle set over it wrench the screw out together with its plug of earth, which is thrown aside before the process is repeated. Leonardo notes that a cutter a b slices through the female thread the screw forms in the soil so the earth will not resist being pulled up. At the top, hinge-like fittings and a lock are drawn, with the note that a is the key of that lock.
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Boring a pit with a giant screw and trestle
The auger makes holes underground up to about a braccio and a half deep and a third to a half wide, turned like an auger. When it is driven twice its length into the earth, a trestle set over it and its handle wrench it out with all its earth, which is thrown aside, and the process is repeated until the pit is finished.
Cutter a b freeing the earth's female thread
The cutter a b is made to slice the teeth of the mother of the screw — the female thread the screw cuts in the soil — so that it will not resist when the earth is wrenched out.
a, the key of the lock
At the top of the sheet a lock fitting is drawn, and the note identifies the element a as the key of that lock.