Why does 17/1000 of an inch matter?

In HO scale model railroading, tracks always used to have rails that are 0.100 inches high, even though that’s not strictly to scale. Many model railroaders — mostly those who interpret the word “model” strictly — favor the newer versions, called Code 83 and Code 70 because they’re 0.083″ and 0.070″ respectively, which are more prototypically accurate than 0.0100″. On several of the model railroading newsgroups a fierce discussion breaks out periodically on this subject, usually about Code 100 vs. Code 83. Here are some of the remarks:

I can think of almost no good reason whatsoever to continue to buy, or plan to use code 100 in HO, save for compelling economic reasons, or for trackage that is not modeled and is out of view.

The way I look at it is that code 100 is more then 20% larger then code 83. If I had a boxcar or building that was 20% larger then it should be, it would be out of scale and not look right on my layout. I’m not a perfectionist when it comes to these things, but buying code 83 was a no-brainer for me.

Sure is more durable, if you like to run your trains on 'I' beams...

Code 100 looks really weird after working with code 83/70/55. You can spot it a mile away in photo of models. No matter the cost or minor (theoretical) structural benefits, don't use code 100. Just my humble opinion.

A common reaction among civilians is to wonder why these enthusiasts care so much, but that’s not really a fair question: after all, I don’t ask why Red Sox and Patriots fans care so much, even though I don’t understand it. My question is to ask whether it’s this difference of 0.017" (about one sixtieth of an inch!) is really so visible to the naked eye. I have trouble believing that it is. On the other hand, code 100 is 20% larger than code 83, so maybe the difference can actually be perceived.

Categories: Math, Model Railroading