this image shows pretty clearly what is part of the ISO code that is required: http://en.wikipedia.org/wiki/File:Containernumber.jpg http://en.wikipedia.org/wi

this image shows pretty clearly what is part of the ISO code that is required: http://en.wikipedia.org/wiki/File:Containernumber.jpg http://en.wikipedia.org/wiki/File:Containernumber.jpg the size and type codes aren't used in the check digit, are not required, and are usually displayed on a separate line: http://www.containerking.co.uk/buy-cabins/images/Shipping%20Container%20001.jpg http://www.containerking.co.uk/buy-cabins/images/Shipping%20... anyway, back to the original question, you can't have two containers with the same owner code, same container ID and made unique through the size and type codes the problem is solved because the large shipping firms (ie. the 5 or 6 that control the industry) each have dozens of manufacturing codes. see my answer in the other part of this thread