HO Gauge Locomotives from eras old and new. H0 scale trains first appeared in the UK in the 1930s, originally as an alternative to 00 gauge.In H0 scale, 3.5 mm (0.14 in) represents 1 real foot. In H0, rails are usually spaced 16.5 mm apart which models the standard railroad gauge of 1,435 mm (56.5 in).