Think of the scale that 0 gauge is in where things are nearly twice the size of 00, so the people are twice the height etc. Now consider the narrow gauge version of it which through convenience can be modelled to run on 00 gauge track. This is 0-16.5. The model people on my trains are 0 gauge figures, so the scale I model in is the 7mm scale which is the same scale as 0 gauge.
Now standard gauge models in 0 gauge have a track width of 32mm. The most popuar narrow gauge version in the same scale which in the UK is 0-16.5, but runs on the 16.5mm track width which is the same gauge width that 00 gauge uses, hence I often use 00 gauge and H0 gauge loco mechanisms (H0 is the same gauge width as 00).
[In America 7mm narrow gauge is known as 0n30 and in Europe it is 0e, which are also all running on the same track as 00 does].
I hope this helps.
I will add that there are advantages and dissadvantages to modelling in 0-16.5.
Advantages are (Depending on ones approach) that as it tends to be easier to scratchbuild and kitbuild in the larger scale, one has the real potential to model to a very limited budget because though ones locomotives may overall cost a little more (Example I may buy a Smallbrook locomotive body kit and a donor 00 gauge locomotive so this bit has cost me more), the real budget advantages are when it comes to the rolling stock because as I make my own couplings, and use readily available cheaply obtained materials (Sometimes free), the main cost of the build are the wheels, and if one is not too fussy, often 00 gaugers will change their wheels to nice finescale metal wheels where the sligtly coarser scale old wheels which could be plastic or metal can come ones way sometimes free (Which I have been really greatful for), or at a much reduced price... And as one is modelling in a larger scale anyway, if they do have larger wheel flanges it does not make them look so bad.
Making ones own waggons is actually easier then one may believe once one has learned how to make a simple chassis.
So I can probably build two or three waggons for the same price that a 00 gauge wagon would cost, so the savings can be quite noticeable.
Now another advantage is that if one bases ones railway on a small narrow gauge railway, one can also save space because if one keeps to smaller locos and stock which isnin keeping with such narrow gauge lines, the actual space on the layout can be less then a standard gauge 00 layout. Not only that, but as narrow gauge railways were often built to reach areas in which only very sharp curves could be used, one can take advantage of this and model curves that can be sharper then 00 gauge first radius curves, so ones layout "Footprint" has the potential to be smaller then a typical small 00 gauge layout if one so desires.
The main dissadvantage is that one has to build most things oneself. One can use 00 gauge track and hide the sleepers under a layer of ballast or one can buy 0-16.5 track by Peco which cost a little more then 00 gauge track which is probably because 00 gauge is more popular, or one can make ones own track which can save more money again (Especially if one builds ones own points), but it can be time consuming as if one concentrates, a typical scratchbuilt point takes me about an evening to build.
IMG_20180529_184528.jpg
