hand pallet trucks allow picking up pallets as low as 25 mm. Steel pallet Steel pallets are strong and are used for heavy loads, high-stacking loads, long term dry storage, and loads moved by abusive logistic systems. They are often used for military ammunition. Metal pallets make up less than 1% of the market. Materials include carbon steel, stainless steel, and aluminum. Of these, carbon steel offers excellent durability at the lowest cost. Stainless steel doesn't require a paint coating, and is preferred for such applications as clean room environments. Carbon steel units are expensive compared to wood, and stainless and aluminum cost about 2–3 times that of carbon steel. Long term costs, however, can be lower than wood. General advantages of metal pallets are high strength and stiffness, excellent durability, resistance to bugs, the absence of splinters, sanitization, and recyclability. Disadvantages include a higher initial price, significant weight, low friction, and susceptibility to rusting (in the case of carbon steel). Metal is primarily used in captive or closed loop environments where durability and product protection are key performance requirements. Metal units today are increasingly price competitive and lighter in weight. Primary industries that use metal pallets include automotive, pharmaceutical, lawn tractors, motorcycles, and tires. Aluminum pallets are stronger than wood or plastic, lighter than steel, and resist weather, rotting, plastic creep and corrosion. They are sometimes used for air-freight, long-term outdoor or at-sea storage, or military transport. History Skids date back to Ancient Egypt and Ancient Mesopotamia, at least as far back as the 1st millennium B.C. The development of the forklift and the needs of World War II logistics operations led to substantial use of pallets. References to the early modern pallets types are slim with a string of patents showing parts of the development. The earliest may be a U.S. patent on a skid from 1924 describing Howard T. Hallowell's "Lift Truck Platform". In the late 1930s, pallets became more commonplace with the newer forklift types. George G. Raymond and William C. House filed for a patent in 1937 (granted US Patent 2178646 in 1939) for a pallet designed to complement a new pallet jack design; the essential features of both are still in common use today. A 1939 patent from Carl Clark shows a type of pallet with steel stringers. Wartime developments were often patented just after the war, so there is a patent from Robert