LEONARDO DA VINCI - Inverted screw

Madrid Ms. I (BNM), fol. 58r

"The inverted screw is a screw in which the threads begin in the middle of its length, and departing from the middle, terminate at the opposite ends of the screw. ... If you turn the inverted screw by both contrary and varied motions, their nuts will also have contrary and varied motion between them."

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