Have you figured out scale and gauge are not the same thing?
Ho is a bit over 16. mm gauge ( width between rails)
S gauge would be 22.5mm, 7/8 inch
O gauge 32mm 1.25".
Full O scale in America is 1:48, but can vary from 1:43-1:64. 1:64 is S scale
Representing narrow gauge there is On30, O scale on narrow gauge HO track.
OO is run on HO track but the stock is modeled at a different scale.1/76
10mm / Fn3 are 1:55 if your looking at something other than the above! !??