Two distinct different mill types:

The Attritor Mill by Union Process uses agitation of grinding media. These heavy duty mills are used both in dry as well in slurry milling. Most applications mill down to few microns particle size, as well as sub-micron with the horizontal small media mill.  Thousands of attritors have been in production since it's launch in the late forties. Many of it's clients are multi-nationals producing ceramics, pigments, inks, chemicals, glass frits as well as chocolate. 

The Roller Mill of MPE uses stacked stages of roller pairs to grind and mill down free flowing dry solids to any narrow particle size distribution from 100 micron up to few millimeters, depending on product requirements.  Market leader for coffee grinding due it's superior temperature control and heavy duty and reliable machine design.