"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?

In the early part of the 20th century, model railway gauges standardised on
Gauges 1, 2 ,3 & 4, which were based upon inch sizes. However, the
standardisation was on track gauge, to allow enthusiasts to use each other's
tracks, rather than on a specific scale. For example, Gauge 1 is normally
1:32 (3/8in = 1ft), but scales of 1:24 and 1:22.5 are also used, to allow it
to represent 3ft6" and 1 metre narrow gauges as well.

By the 1920s, railways were moving indoors, so a smaller scale than Gauge 1
was needed. That lead to Gauge 0 1/4in = 1 ft, with a track gauge of 1.25".
However, that gives a scale track gauge of 5ft, so the scale was redefined
to 7mm = 1ft, to bring the track to a scale 4ft 8.5ins.

Colin Bignell