A short course in Railroading ... For Airline executives (by Southern Pacific 1946)

[Trinity River Bottoms Boomer]

M636C: Thanks for clearing up the "battle of model railroading gauges".  Once in awhile I visit www.proto48.org where O scale modelers use correct standard gauge track for their modeling.  I've always wondered about HO vs. OO though.  I dare not ask about G though.  'G'ads, here we go again....LOL 

[Overmod]

M636C

HO models are 1/87 and the 16.5mm gauge is correct. ... The British build O scalle models to 1/43.5 (exactly twice HO) which gives the right gauge with O gauge track.

A bit more complicated.  HO is that rare bird, hated by SI types: a metric standard relative to English measure.  (It.s exactly 3.5mm to the foot)  So the 16.5mm gauge is reasonable for 4/8.5" but ought to be slightly narrower ... not that for practical purposes the rounding-up error is very great.

I am not familiar with British O but my understanding was that it is actually of German origin, and is exactly 43.5 scale (the 'letter' originally being not an O but a 0 in the same system as current 'Gauge 1').  Whether there is as I suspect a similar concession to 7mm-to-the-foot, I can't say.

Say, this has almost as much to do with airline executives as direct-drive steam turbines had to do with ... what was that topic, again?...