Williams offers a complete line of one-way and reversible primary. Depending upon the feed and product desired, a primary shredder can be the only size reduction involved or it can serve as a preparation, or coarse product, mill. Reversible Shredders Williams Primary.The Electric Automatic Laboratory Mortar Grinder Mill Model 911MPEMG100 is used to reproducibly grind, homogenize and mix a wide range of solid materials in dry wet or cryogenic condition. The material to be processed falls into the Pulverizing area between Mortar and Pestle by top feeding via the opening which is at the inlet cover. The material is then pulverized and mixed between the.