See also: Mill
in Pictorial Dictionary of Heraldry.
A grinding stone attached to a wooden pole that allows it to be turned, grinding grain to flour.
Default orientation: horizontal stone with axle to chief. Proper coloration: gray or argent stone.
Source: Siebmacher’s Wappenbuch of 1605. Artist: Johann Siebmacher. (Arms of Uhrmuhl, page 98.)