Wheel with straight and reversed teeth driving screw-nuts
A toothed wheel set between two like mechanisms so their teeth act in alternation on the nuts of screws
The main drawing shows a large machine built around a great wheel and a vertical screw. Leonardo notes that a wheel with straight and reversed teeth is used to drive the 'female' threads (nuts) of screws, and specifies that this wheel should stand between two similar mechanisms so that, when the teeth on one side cease to engage, an equal number of teeth on the opposite side continue the work with the other mechanism. A detail at the upper right shows the two toothed elements and their engagement. Substantial further text on the sheet is not included in the transcription.
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Wheel with straight and reversed teeth driving screw-nuts
A wheel carries straight and reversed teeth that move the 'female' threads (nuts) of screws; the detail at the right shows the arrangement of these teeth.
Wheel set between two mechanisms for continuous drive
The wheel is to stand midway between two similar instruments so that, when the office of the teeth on one side fails, as many teeth on the opposite side keep performing the office with the other instrument.