"4square" wrote in message
oups.com...
A pal of mine is a keen railway modeller, and we have often wondered,
how the scale for 'O'- gauge ever came to be set at 7 mm to the
imperial foot. The track gauge is 32 mm, which is about right for 4
feet 8.5 inches. Anyone any ideas?

and here's another link which points out that early Hornby trains weren't to
scale:
http://www.hrca.net/o_gauge_factsheet.html
looks like it just evolved over time rather than at any one point in time.
Hugh