To determine the size of mill drive required, factors such as the diameter and weight of the jar mill should be considered the largest diameter jar that could be used on this series of roll drives is a 10″ diameter jar, the length of the jar and the number of grinding jars to be used simultaneously. If it were desired to grind four 5″ diameter by 8″ long jars at one time, 4 x 8″ + 2″ (Space Between Jars) = 40 inches of roll length required. Either a two tiered 24″ long roll drive (4 – 24 inch long rolls) or a single tier 48” roll drive would provide the space required.