O Scale

O scale (or O gauge) is a scale commonly used for toy trains and model railroading. Originally introduced by German toy manufacturer Märklin around 1900, by the 1930s three-rail alternating current O gauge was the most common model railroad scale in the United States and remained so until the early 1960s. Scale  is 7 mm to 1 ft – 6.35 mm to 1 ft. Scale ratio     various: 1:48 to 1:43.5  Model gauge     30 mm (1.181 in) – 33 mm (1.3 in)