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From: stimac@tymix.UUCP (Michael Stimac)
Newsgroups: net.railroad
Subject: Identifying narrow gauges in model rr's
Message-ID: <179@tymix.UUCP>
Date: Thu, 9-Feb-84 15:41:04 EST
Article-I.D.: tymix.179
Posted: Thu Feb  9 15:41:04 1984
Date-Received: Sat, 11-Feb-84 09:23:04 EST
Organization: Tymshare Inc., Cupertino CA
Lines: 34

Yes, the numbers in the gauge designations refer to the number of feet
in the prototype gauge, thus, e.g.:

On3 means O scale, narrow gauge, 3 foot width, and
HOn2 means HO scale, narrow gauge, 2 foot width.

Related comments: 

There is such a thing as 2 1/2 foot gauge, this is written as On2 1/2,
for example.  There exist a variety of odd inch gauges, and these would
be written as HOn42", for example.  There is also the possibilty of a
wide gauge, which I have seen written as HOw6, meaning HO scale, wide 
gauge, 6 foot width. The original Erie Railroad was to this width, and
many railroads in the US southeastern states also were wide gauge before
the Civil War (I don't know the precise year of change, but the conversion
to standard gauge is supposed to have taken place in a single day).
In Europe, narrwo gauge lines often use a width a one meter, and this
is written as HOe. 

Notice that the abbreviations O, HO, N and so forth refer to scales,
not gauges. When written by themselves it is implicit that standard
gauge (4' 8 1/2") is referred to. Unfortunately, the letters can be
used to reefer to several close, but different scales. For instance,
O scale work may be done in 1/4" = 1 foot, 17/64" = 1 foot, and in
7mm = 1 foot.  Notice that the common HO scale is exactly half of
the 7mm figure, thus the name H(alf) O.

There is a lot more to the scale/gauge story. Anyone interested?

Michael Stimac
Tymshare, Inc.
Cupertino, CA    ...hplabs!oliveb!tymix!stimac