This is the story told on another forum:
I'm especially interested as my dad worked for A & P / Tube Investments in the 50s in Oldbury and he told me about when a US Co. sent A & P the ''smallest calibre tube in the world'' and they sent it back without a comment attached. Eventually a US engineer weighed it and found that it was a very small amount heavier than a piece of the same length of tube that the US Co. had not sent. Then in US, they put some sophisticated eqpt to work on the sample returned by A & P. To everyone's surprise, the calibre was now smaller but they could get no further...all the metal was the same, so they contacted A & P who told them ''after measuring the exact length of it, we put another tube inside your ''world's smallest tube'', then annealed them so there was no visible join''. .
And then the killer ''Please find loosely enclosed in a stoppered bigger metal tube, a section of the tube that was put inside your tube - inside that a still smaller tube..."