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. Roll Speeds for 2.5″ Diameter Roll Drive