There will be a hopper on top into which you feed the nuts. A crank or paddle inside rotates, pressing the nuts against a grater inside. The ground nuts then fall through down into a receiving receptacle.
Many come apart for easier cleaning.
A Nut Mill is better to use for grinding nuts than a food processor because it doesn’t release the oils and turn them into nut paste.
Commercially, nut mills can also be designed to press oil out of nuts to make nut oils.
Mortar and pestle, food processor (but be very cautious or you will end up with nut butter). To better your chances in a food processor, freeze the nuts first, and use only the pulse button.
A Nut Mill constructed from stone in Sainte-Nathalène, France, dates from the 1500s; it is operated by water and is used to make walnut oil.
A “nut mill” was also used as the name for the press that crushed apples for apple cider. It got its name from the nuts that constituted its working parts. The apples would then be passed through onto the actual cider press.