A burr mill, a type of crusher having a revolving and a stationary abrasive surfaces, separated by a distance usually set by the user. The device includes a revolving screw that pushes the material past the abrasive surfaces. Both electrically and manually powered models exists.
The most readily available example of a burr mill is a vintage coffee grinder. Mesh size obtained varies mill per mill, but a good mill at closest possible distance of the surfaces, will yield ca. -40 mesh. Burr mill is best suited for milling hard and brittle materials, such as charcoal and hexamine (eg. 'Esbit' brand) fuel tablets.
One must bear in mind, that burr mills must never be used to mill any explosive mixture or a friction sensitive chemical. Doing so will very likely result in an explosion of the mill, due to the tremendous friction at the surfaces.