P4 gauge

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P4 standards, also known as Protofour standards, are a set of measurements that allow the accurate construction of a model railway to 4 mm to 1 foot scale. For standard gauge track these standards translate to a scale model track gauge of 18.83 mm.

As the name implies, P4 is accurate to scale for 4 mm to 1 foot scale modelling, while other track gauges such as specified for 00 (16.5 mm) and EM (18.2 mm) when used for standard gauge prototypes portray 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.

P4 standards are promoted in the United Kingdom by the Scalefour Society.

Due to space constraints and the necessity for the construction in model form of tighter than prototypical track curves there are still a couple of compromises within P4 standards. For some railway modellers who feel that this is unnecessary an exact set of standards has been formulated and are known as Scalefour standards also known as S4. These standards are not to be confused with the Scalefour Society.

P4 is only used to potray railways of the United Kingdom in Britain. However the 5'3" Irish broad gauge can also modelled in 4 mm scale with 21 mm gauge track to P4 standards.