HO Scale

HO or H0 is a rail transport modelling scale using a 1:87 scale (3.5 mm to 1 foot). It is the most popular scale of model railway in the world.[1][2] The rails are spaced 16.5 millimetres (0.650 in) apart for modelling 1,435 mm (4 ft 8+1⁄2 in) standard gauge tracks and trains in HO.[3]

The name H0 comes from 1:87 scale being half that of 0 scale, which was originally the smallest of the series of older and larger 0, 1, 2 and 3 gauges introduced by Märklin around 1900. Rather than referring to the scale as "half-zero" or "H-zero", English-speakers have consistently pronounced it /eɪtʃ oʊ/ and have generally written it with the letters HO. In other languages it also remains written with the letter H and number 0 (zero); in German it is thus pronounced as [ha: 'nʊl].