"Quern-stones are stone tools for hand-grinding a wide variety of materials. They are used in pairs. The lower, stationary, stone is called a quern, while the ...
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upper mobile stone is called a muller or handstone. The central hole is called the hopper and a handle slot enables the handstone to be rotated. They were first used in the Neolithic era to grind cereals into flour." - (en.wikipedia.org 03.03.2020)
