The earliest hand-operated cranks appeared in China during the Han Dynasty (202 BC-220 AD). They were used for silk-reeling, hemp-spinning, for the agricultural winnowing fan, in the water-powered flour-sifter, for hydraulic-powered metallurgic bellows, and in the well windlass. The rotary winnowing fan greatly increased the efficiency of separating grain from husks and stalks. However, the potential of the crank of converting circular motion into reciprocal motion never seems to have been fully realized in China, and the crank was typically absent from such machines until the turn of the 20th century.