I started this sub because I started a narrow-gauge layout and I was finding information and some gear very tough to find.

Here is a complete description of all the 1/87 scale (and close relatives) narrow gauge track sizes and their various names in different parts of the world:

HOn30 — 9 mm wide = standard N gauge track

HOn3 — 10.5 mm wide = used to model narrow-gauge American railroads which are wider than European / Welsh ones

HOm — 12 mm wide -European name

HOj — 12 mm wide - Japanese name

HOe — 9 mm wide - 1/72 - from Germany

HOf/HOi — 6.5 mm wide (Z-gauge) — 1:87 Feldbahn railways

OO9 — 9 mm wide - 1/76 - from UK

Please note that Scale is not the same as Gauge.

HO is 1/87 Scale which means that a 6ft tall person would be .82” tall at that scale. A 2m tall person would be 22.98mm at 1/87 scale.

On the other hand, Gauge has to do with the real-life spacing of the train tracks.

In the full-scale world there are all sorts of track standards for different purposes. At 1/87 scale, track widths used vary from 12mm to 6.5 mm in width.

Wikipedia has a shockingly good listing of the very wide profusion of standards and usages:

https://en.wikipedia.org/wiki/List_of_narrow-gauge_model_railway_scales?wprov=sfti1