structural:summarization, linguistic:voice_change
Millstones or mill stones are stones used in gristmills, used for triturating, crushing or, more specifically, grinding wheat or other grains. They are sometimes referred to as grindstones or grinding stones. Millstones come in pairs: a stationary base with a convex rim known as the bedstone and a concave-rimmed runner stone that rotates. The movement of the runner on top of the bedstone creates a "scissoring" action that grinds grain trapped between the stones. Millstones are constructed so that their shape and configuration help to channel ground flour to the outer edges of the mechanism for collection. The runner stone is supported by a cross-shaped metal piece fixed to a "mace head" topping the main shaft or spindle leading to the driving mechanism of the mill.