From:
https://www.atc-mechanical.com/tube-...size-overview/
Quote:
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"Tubing is measured by the OUTSIDE DIAMETER (O.D.), specified in inches (e.g., 1.250) or fraction of an inch (eg. 1-1/4″). Pipe is usually measured by NOMINAL PIPE SIZE (NPS). .... For sizes from 1/8-inch through 12-inch, the NPS corresponds to the nominal inside diameter, but differs somewhat from its actual inside diameter. Early pipe manufacturers made the walls in the smaller sizes much too thick, and in correcting this error in design, they took the excess from the inside to avoid changing the sizes of the companion fittings."
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From memory, I think the AEDB record refers to pipe rather than tube for the bows but you should confirm this (feel free to correct me if this isn't true).
I have the impression that someone gave you at least a partial bow (unless it was a replica?). Don't ask me where it might be squirreled away "for safe keeping". If that can be found and measured it could be compared to the tables of tube and pipe size to find the nearest modern equivalent.
No proof of this but I doubt the originals would have been as light as modern EMT (electric conduit) - maybe the standards on that have changed over time too...
Other possibly useful links:
http://www.wermac.org/pipes/pipe_vs_tube.html
https://www.commercemetals.com/tube-...plain-english/
https://www.metalsupermarkets.com/di...pipe-and-tube/
I know Metal Supermarkets aren't the cheapest but their site can be a guide to what is reasonably easy to buy off the shelf in Canada (or USA).