A grindstone is a stone disc mounted on an axle, with a crank for turning; it’s used for sharpening knives and other blades. The grindstone is a period charge, found in the canting arms (Italian mola) of da Molla, mid-15th C. [Triv 227].
The term “grinding wheel” is a Society blazon for a grindstone mounted in a wooden frame for use, as seen in an image in the Romance of Alexander, c.1340. As a charge, it appears to be unique to the Society. For related charges, see mill. See also rock (millstone), wheel.
Wolfric Hammerfestning bears: Azure, a grinding wheel between three axes reversed argent.