Stone mill introduction: Stone mill is an important tool for the Qiang people to process grain. It is divided into two types: hand grinding and water grinding. The hand mill is a stone mill driven by hand; the water mill is a stone mill powered by water energy, and there are two types: horizontal and vertical. It is generally believed that it was invented in the Jin Dynasty and is related to Du Shi's invention of water drainage. The invention of the mill greatly improved the efficiency of agricultural production of the ancient Qiang people. Even today, this ancient invention is still used in many places.