Hobbies And Interests
The Term Itself
HO is not pronounced “hoh.” Rather, it is an Americanization of H0 (the letter “h” and the number “0”) and is pronounced as the letter “h” followed by “oh” (h-oh). HO scale was originally created in the United Kingdom as an alternative to 00 (double zero) scale, but it never caught on there. HO is approximately half the scale of the popular 0 (zero) scale, hence the “half zero” or H0 designation in the UK.
International Scale
Because of its origin in the UK, HO is a metric scale. While it means that 3.5mm of the model represents 1 foot in the “real world,” HO is often converted to American units of measure--most commonly as 1:87 scale, which means the real item is 87 times larger than the model. (This is a simplified ratio; the most accurate ratio would be 1:86.086, far more accurate than necessary for most discussions.)
Scale vs Gauge
There is an HO scale and an HO gauge, which confuses some people. According to Ross Crane, scale is the difference between the size of the model and the original, while gauge is the distance between the rails of a model railroad track. As stated earlier, HO is roughly a 1/87 scale model of the real thing. HO gauge is roughly 0.649 inches (56.5-inch real track divided by 87), or 16.5mm. (The metric measurement is cited by Carl Arendt at his Small Layout Scrapbook site.) HO scale trains use HO gauge track, but the two measures mean two different things.
HO Slot Cars
According to HOSlotCarRacing.com, slot cars have never actually been built to HO scale, although they are generally referred to as HO-scale cars. Early slot cars were built to the popular double-zero (00) British scale of 1:76. Later models were built to even larger sizes, 1:64 and 1:32 being popular scales.
HO Diecast Metal Cars
HO is a popular scale for collectable diecast metal cars. It is also popular for small models intended for extra realism in HO railroad layouts, where entire dioramas are frequently built as showpieces for the trains.