Most retail products are packed in a hierarchy of packaging. These containers fit into boxes that are about one cubic foot in dimension and are unloaded, item by item, by the person stocking the shelves. These boxes in turn are handled on pallets, wooden platforms about 6 inches high and 40 inches by 48 inches along the top. Pallets are loaded two or four boxes high and moved by mechanical devices known as forklift trucks, tractorlike vehicles with two lifting prongs in front that fit into slots in the pallet and then lift it. Goods that are not packaged are often handled in bulk.
Examples are iron ore, coal, and grains that move in trainload, truckload, and shipload lots.
They are loaded, unloaded, and transferred by large mechanical devices. Liquids such as petroleum are pumped through pipelines or carried in vessels called tankers.