One of the first things to decide in building a model railroad is the scale, or gauge, you want to use. Two of the most interesting gauges in use today in the United States and Canada are “OO” (1/76) and “TT” (1/120). Each has certain advantages.

“TT” uses ½” gauge and is very good when operating space is limited. It lacks detail, however.

The “OO” uses a ¾” gauge. The American “OO” must not be confused with the English. The English use the same size track as the “HO,” but increase the size of their models slightly—whereas the American “OO” uses ¾” gauge. This gauge can truly be called an American and Canadian gauge because it was first used on this side of the Atlantic. It originated because early model railroaders, in search of a smaller gauge than the standard or “O,” found that more detail and smoother operation could be obtained by slightly increasing the English “HO” size.

The advantages of “OO” gauge are manifold. First in importance is the amount of detail that can be obtained. There is hardly a part on the exterior of the modern locomotive or car that cannot be duplicated on the “OO” gauge size. Another advantage of “OO” gauge is that a great many manufacturers produced this size equipment and as a result the model railroader can obtain car kits in greater variety and for practically any model he desires to follow.

[OK, this post is actually the April fool’s post for 2009. However, it is closely based on the text in the 1937 Scale-Craft catalog, which compared HO, OO, and O gauges. The models in the photo are an OO gauge Scale-Craft 4-6-0 and a HP Products TT gauge 0-6-0 that I rebuilt (I have a very limited number of TT models). Also we have OO, HO, TT, and N scale box cars lined up for a size comparison. As always, click on the photos for a larger view. TT really is an interesting size with as much or more produced in terms of variety than in American OO, but in the post WWII era, and it is still produced today in the former Eastern Europe. TT has less collector interest—there was no major maker comparable to Lionel in TT.]