There are three different versions of the "O" scale, each of which uses tracks of 32 mm for the standard gauge. The American version follows a dollhouse scale of 1:48, sometimes called "quarter-gauge" as in "one-quarter-inch to the foot". The British version continued the pattern of sub-contracting to Germans, so, at 7 mm to the foot, it works out to a scale of 1:43.5. Later, the European authority of model railroad firms MOROP declared that the "O" gauge (still 32 mm) must use the scale of 1:45, to allow wheel, tire, and splasher clearance for smaller than realistic curved sections.