Open top container

An open-top container is a standard-dimension box with no fixed steel roof, closed instead by a removable tarpaulin stretched over arched roof bows. It loads from above by crane for cargo too tall or awkward for the door opening: machinery, glass, timber, and tall project pieces. The header bar over the doors is usually removable to clear the loading path. Built to ISO 668 and ISO 1496-1 in 20-foot and 40-foot lengths, the box stays wind-and-water-tight once the tarpaulin is roped and sealed. Type code 22U1 marks a 20-foot open-top unit. Out-of-gauge height is declared because the cargo can break the roof line.