OO is just a slightly bigger scale (1:76) at H0 track. Since UK loading diameter is slightly narrower than on other standard gauge railways (which is the reason for there being OO at all, as H0 motors wouldn't fit models of UK locomotives), there wouldn't be much of a noticeable difference. To me, this looks bigger than H0, but there are other scales and gauges, as well. Admittedly, my knowledge about these is pretty limited.
