OO gauge or OO scale (also spelled 00 gauge and 00 scale) model railways are the most popular standard-gauge model railway tracks in the United Kingdom. This track gauge is one of several 4 mm-scale standards (4 mm to 1 foot or 1:76.2) used, but it is the only one to be served by the major manufacturers. Despite this, the OO track gauge of 16.5 mm (0.65 in) is inaccurate for 4 mm scale, and other gauges of the same scale have arisen to better serve the desires of some modellers for greater scale accuracy.