Is HO the most popular model train scale?
HO is a gauge (scale) for model trains. The name HO comes from
the fact that it represents a reduction of half from the earlier O
gauge ("Half O"), which was more popular in Europe. The ratio for
HO gauge equipment is 1:87 which means that the HO tracks are
16.5mm apart, or 1/87th of a standard train track (1435mm). In
Europe, an almost exactly the same scale is called OO (pronounced
"Double O"), even though it is much closer to half of O scale than
double it (it is actually called "Double O" because there are two
O's (OO) in the scale name).