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Screw, simple machine consisting of a cylindrical or conical body around which is wrapped a spiral plane or thread, and used as a fastener, propeller, and part of many more complex machines. Screws were developed by the ancient Greeks and used in presses (to extract oil or juice) and weight-lifting devices. They came into wide use as fasteners in the 1500s, with major refinements in the 1800s including the development of the sharp-tipped wood screw. Screws that modify force and motion, such as are used in vises and drilling tools, are called power screws.

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21st Century Webster's Family Encyclopedia21st Century Webster's Family Encyclopedia - Sato, Eisaku to Serra, Junípero