It may sound dum but I cannot keep it straight in my head the difference between O Gauge Curve ie:072 vs O Scale Curve 54 Radius. If a locmotive requires 072 curve is that scale or gauge and what would be the minumin scale radius that locomotive could operate on with out problems. I am building a layout and keep getting them confused. Can somebody explain it to me. HELP!
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Track descriptions that have the zero in front, like 027, 054, 072, etc. are diameters. That's the "width" of a full circle. The easy way to remember this is that the zero looks like a circle. A curved piece of track described as 072 will create a circle of track 72" across, if extended all the way around.
Scale folks refer to radius, and the radius of a circle is half-way across the diameter. They say 36" radius, 48" radius, etc.
So, a curved track called 072 is a 36" radius curve. (36 is half of 72)
For the most part it depends what your modelling,typically, a 48" radius would be for a 2-rail o guage locomotive, an o-48 would be for a 3- rail o guage locomotive. Manufacturers like MTH that offer similar locomotives for 2 or 3 rail, usually give the minimum curve description for both track types.
Gentlemen Thank You very much. Mr Bloom I think that is the easiest and best way to remember the difference. Thanks again every one.
Hey how did this post get so wide
apparently when I posted the google link the hoop-la program did not keep the format.
I think the confusion comes in because HO and N all talk in radius, not diameter. 
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