I have owned a quern, or rather a quarter quern for many years, I use it as doorstop. When complete it was a squat cone or mushroom shape, with a tapered hole through from the top to where the stalk would have been. This stone sat upon another levelled stone, the two pegged together at the middle so the top stone can be rotated clockwise and anticlockwise by hand. Grain introduced through a slot in the peg in the hole passed down and between the stones where it was ground to flour passing out around the edge. Common from Roman times these hand mills went out of use, indeed were, so I have heard, made illegal, whenever a local landowner built a wind or watermill, solely in order to ensure their market. Thus whole querns are rare as they were invariably smashed and half, or rather quarter, ones, such as mine relatively common.