P4 gauge
P4 gauge, also known as protofour, 4mm finescale, and S4 is a model railway standard of 4mm scale and accurate 18.83mm gauge track. As the name implies, P4 gauge is accurately to scale for 4mm scale modelling, while other track gauges (such as OO gauge and EM gauge) used for standard gauge prototypes are less accurate approximations.As well as a track gauge, P4 also specifies the exact wheel profile and track parameters to use, which are largely an exactly to scale version of real life standards.
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