Screwsholdthingstogether.Theyalsodigholesandsavespace.Buttheycanalsomove things.

Thinkaboutthedrillbitspinningintothewood.Woodshavingscomeoutofthehole.Thegroovesbetweenthethreadscarrythepiecesofwoodupalongthe bit. 

Thisexplainshowa2,000‑year-oldinventionworks.Ascrewliftedwaterfromarivertowater crops.

Alargescrewwasfittedinsideatube.Oneendofthetubewasplacedinariver.Aworkerturnedacrankononeend.Theturningthreadsofthescrewpushedthewaterupthetube.Theydumpeditoutattheotherend.Thewaterflowedalongditchestofields.Archimedes’screw,namedafteritsinventorinancientGreece,hasstoodthetestoftime.Peoplestilluseit today!