Runner stone

Millstones or mill stones are stones used in gristmills, for grinding wheat or other grains.

Millstones come in pairs. The base or bedstone is stationary. Above the bedstone is the turning runner stone which actually does the grinding. The runner stone spins above the stationary bedstone creating the "scissoring" or grinding action of the stones. A runner stone is generally slightly , while the bedstone is slightly . This helps to channel the ground flour to the outer edges of the stones where it can be gathered up.

The runner stone is supported by a cross-shaped metal piece (rind or rynd) fixed to a "mace head" topping the main shaft or spindle leading to the driving mechanism of the mill (wind, water (including tide) or other means).

Neolithic and Upper Paleolithic people used millstones to grind grains, nuts, rhizomes and other vegetable food products for consumption. These implements are often called grinding stones. They used either saddle stones or rotary querns turned by hand. Such devices were also used to grind pigments and metal ores prior to smelting.

In India, grinding stones (Chakki) were used to grind grains and spices. These consist of a stationary stone cylinder upon which a smaller stone cylinder rotates. Smaller ones, for household use, were operated by two people. Larger ones, for community or commercial use, used livestock to rotate the upper cylinder.

The type of stone most suitable for making millstones is a siliceous rock called (or buhrstone), an open-textured, porous but tough, fine-grained sandstone, or a silicified, fossiliferous limestone. In some sandstones, the cement is calcareous.

Millstones used in Britain were commonly of two types:

In Europe, a third type of millstone was used. These were uncommon in Britain, but not unknown.

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