Editing 4 mm scale (section)

==Standard gauge==
Three different gauges are used for modelling [[standard gauge]] railways in the [[United Kingdom]].

===OO gauge===
[[OO gauge]] uses 4&nbsp;mm scale with 16.5&nbsp;mm [[Rail gauge|gauge]] track,<ref>{{Cite web |title=Standards |url=https://doubleogauge.com/standards/ |access-date=2022-03-31 |website=The Double O Gauge Association |language=en-GB}}</ref><ref>{{Cite web |date=2019-06-07 |title=What is OO gauge? |url=https://www.world-of-railways.co.uk/techniques/what-is-oo-gauge/ |access-date=2022-03-31 |website=World Of Railways}}</ref> which is inaccurately narrow since it is correct for [[HO scale]] (1:87.1). It is the most popular standard in the UK for 4&nbsp;mm scale trains<ref>{{cite web |title=OO gauge |url=https://www.fabtintoys.com/oo-gauge/ |website=Fabtintoys |publisher=Fabintoys |access-date=12 April 2022}}</ref> and is produced by the two main manufacturers in the UK. The traditional standard for wheels and track is a very coarse one with extremely oversize [[Rail tracks|rail]]s and [[flange]]s; in recent years, some manufacturers have switched to using the American [[National Model Railroad Association]] HO standard S-4 instead.

===EM gauge===
[[EM gauge|EM]] was originally defined to use 18mm as the track gauge (hence the name: Eighteen Millimetres). This was revised, and today EM gauge uses an {{RailGauge|18.2mm}} track gauge, which is closer to accurate but not fully to scale.  It was developed as an early improvement on the standard OO system.  It is still popular with FineScale modellers today because it utilises larger than scale flanges on the wheels of rolling stock, and because point and crossing (P&C) work is a little easier due to an overscale flangeway clearance.  These two concessions in scaling down the prototype make for reliable running.  This factor explains the continued popularity of EM as a scale for finescale modellers working today.

===P4===
[[Protofour|P4]], otherwise known as [[Protofour]], or "18.83", is a close to exact 4&nbsp;mm:1&nbsp;ft replica of real-life track and wheel dimensions.<ref>{{Cite web |last=Elliott |first=Russ |title=Scalefour Digest 1.2 'P4 Track and Wheel Standards' |url=http://www.clag.org.uk/p4standards.html |access-date=2022-03-31 |website=www.clag.org.uk |language=en-GB}}</ref> The gauge of track built to these standards is 18.83&nbsp;mm.  Along with EM Gauge It is also a popular choice for finescale modellers working today.  The main advantage of P4 over the other 4&nbsp;mm standards is that the wheel flanges are approximately to scale and the flangeway gaps on P&C work are also close to scale.  This is most noticeable in photographs of the model where in many cases is it almost impossible to detect that you are looking at a model, as opposed to the real thing.  The disadvantages of near to scale flanges and flangeway crossings are that the trackwork has to be laid and built to very close tolerances and needs to be flat.  If this is not the case then the reliability of rolling stock on the trackwork is compromised leading to poor running and derailments.  This problem can, to an extent, be mitigated by the use of some form of suspension system in the locomotives and rolling stock used on the layout. There are different ways to do this and reference to one of the societies supporting modelling to this standard is recommended.{{According to whom|date=February 2024}}