Rail gauge is the distance between the rails, measured between the insides of the heads slightly below the top, as the rail head is slightly rounded, both when new and when worn.
The width of the head of a rail increases as the weight of the rail increases, so it would be problematic to measure the gauge between the centres of the heads of the rail, as formerly in Italy. The Blaenau quarry gauge, on metal bars, was possibly 2ft centre-to-centre; this may have been followed by the FR. At Llanberis this is certainly the case, but the railway was 1ft 10.75in gauge (it is now FR standard). It is an intriguing archaeological finding that the rutways of Roman roads, measured both in Britain and in Italy, are consistently 4ft 10ins centre to centre (or 4ft 8in between the inside edges). That is also the pace of a Roman legionary, left foot to left foot, at 4.855ft; a thousand of these at 4855ft is miles passuum, a Roman mile. The Stockton & Darlington Ry of 1825 was 4ft 8in - the extra half-inch of the standard gauge seems to have been added around 1830 to allow more play for the wheels.
On the Festiniog Railway, the gauge is nominally 2ft, but the -
- actual gauge on straights is 1 ft 11½ ins (597 mm)(Dow 2014), and the
- actual gauge on "sharp" curves is up to 2 ft (610 mm).
In metric terms, the FR gauge is 597mm, but on sharp curves it may increase to 610mm. The wheels have treads wide enough to accommodate these differences.
The complete set of measurements for FR track and wheel-sets is:
Gauge 23½ inches (597 mm)
Back to back wheel measurement 21 inches (533 mm)
Outer rail to check rail gauge 22⅛ inches (562 mm)
Check rail clearance 1⅜ inches (35 mm)
Clearances, wheel to rail ¼ inch (6.35 mm)
Width of tread 3⅛ inches (79 mm)
Thickness of flange 1 inch (25.4 mm)
Gradient of coning 1 in 18
Typical diameter of wheels 18 inches (457 mm)
Inclination of rails 1 in 20 (recent relaying - was nil for chaired and early F/B track - an early reference to using inclined base plates is FRM No. 156 p 468 in 1997.)
Depth of flange 15/16ths (23.8 mm)
Source: Dow A 2014 Appendix F.
Other Railway Gauges
The Gauge Commission of 1845 chose the Stephenson gauge rather than the broader Brunel gauge, but didn't concern itself with gauges narrow than Stephenson's. As a result, narrow gauge (NG) lines, of which the Festiniog Railway was a pioneer, adopted a dog's breakfast of gauges. FR was not affected by the 1846 Act, being incorporated and opened before it came into force. That is why the FR was able to have a passenger service in 1865.
Other UK railway gauges are as follows:
|Railway||Region||Gauge ft.in.||Gauge mm||Earliest
|Romney Hythe & Dymchurch Railway||UK Kent||15⅛ inches||(0384 mm)||1927||AA |
|Talyllyn Railway||Wales||27 inches||(0686 mm)||1866||CC |
|Welshpool & Llanfair Light Railway||Wales||30 inches||(0762 mm)||1903||FF |
|Isle of Man Railway||I of Man||36 inches||(0914 mm)||1873||JJ |
|Glasgow Subway||Scotland||48 inches||(1220 mm)||1896||MM |
|London Transport||UK London||56⅜ inches||(1432 mm but 1435 mm
on ballasted flat
|Network Rail||UK||56½ inches||(1435 mm)||1830||RR|
|Northern Ireland Railways
D&DR 5ft 2in
UR 6ft 2in
D&KR 4ft 8½in
|NI||63 inches||(1600 mm)||
|SS  Converted to |
|Broad Gauge||UK GWR||84¼ inches||(2140 mm)||1838||TT |
|Vale of Rheidol Railway||Wales||23¾ inches||(0603 mm)||1902||UU |
|Corris Railway||Wales||27 inches||(0686 mm)||1859||VV |
|Welsh Highland Railway||Wales||23½ inches||(0597 mm)||1923||WW |
|Croesor Tramway||Wales||24 inches||(0610 mm)||1864||XX  Horse drawn|
|Penrhyn Quarry Railway||Wales||22¾ inches||(578 mm)||1798||XA |
|Snowdon Mountain Railway||Wales||31½ inches||(0800 mm)||1896||XD  Abt rack.|
|Snaefell Mountain Railway||I of Man||42 inches||(1067 mm)||1895||XG  Fell "rack".|
|Bala Lake Railway||Wales||24 inches||(0610 mm)||1972||XJ |
|Brecon Mountain Railway||Wales||23¾ inches||(0603 mm)||1980||XK |
|Fairbourne Railway||Wales||12¼ inches||(0311 mm)||1980||XL |
|Llanberis Lake Railway||Wales||23¾ inches||(0603 mm)||1971||XM |
|Festiniog Railway||Wales||23½ inches||(0597 mm)||1836||XP |
|Manx Electric Railway||I of Man||36 inches||(0915 mm)||1893||XQ |
|Padarn Railway||48 inches||1843||XR |
- personal observation and measurement
- personal observation and measurement while on PW track gangs
- Wikipedia: British narrow gauge railways
- Wikipedia: British Narrow Gauge Slate Railways
- Wikipedia: Great Little Trains of Wales
Newspaper articles in far off N S Wales reported, or misreported, even more gauges for the Festiniog Railway than the FR ever had, including:
|Gauge||Tags 1||Tags 2||Comment||Earliest
on "Sharp" Curves
Mistakenly assumed to be "Normal" gauge
|2ft 0in||14||87||Rounded Gauge||1864||PP |
|2ft 1in||1||1||Rounded Gauge with muddled
widening on sharp curves.
|2ft 6in||3||11||Incorrect||1867||EE  Ample. |
|2ft 9in||1||2||Incorrect||1871||TT |
|3ft 0in||1||Proposed for Light Rail||TV|
|First Railway QLD||1865||SS|
|Pre-railway TAS||1869||TW |
|5ft 3in||First Railway TAS (BG)||TX ; so as to share designs with Victoria|
|3ft 6in||Second Railway TAS (NG)||1876||UU ; probably influenced by Pihl and Queensland|
|2ft 0in||Third Railway TAS (TG)||UX ; possibly influenced by Fairlie and FR ; mountainous terrain.|
|3ft 6in||First Railway WA||1879||HH|
|10||Festiniog Quarry (slate)||1850||FQ|
|2ft 3in||2||Talyllyn Railway||1951||TT |
- Note: Tags = Number of Tagged NLA Newspaper Articles ; this is a work in progress.
- Note: NLA=National Library of Australia.
- Note: (QNNA) "Sharp" curve means less than ______ chains radius.
- Note: The dates of the "First Railways in" are to help tell if the NG FR influenced the selection of Narrow Gauge (NG) in those colonies.
- Note: Number of tags means number counted "so far". Needs to be manually updated from time to time.
- Note: It is difficult to search for "1ft 11 1/2", etc. These strings need to be tagged/bookmarked whenever you come across them.
This article is incomplete.
The following terms are a bit ambiguous:
- toy 
- Tom Thumb
Some sources cast doubt on the relevance of the Festiniog system, probably for reasons including:
- heavy traffic, several trains per day; hard not to make money
- freight rates higher per mile for narrow gauge than for standard gauge; hard not to make money ; politically unsuitable for government railway.
- heavy traffic mostly goes downhill with continuous gradients ; would other Horse railways be so fortunate?
- transhipment is mainly to ships at Portmadoc, and relatively little transhipment between narrow gauge and standard gauge.
- very low speeds on FR:
- even on straight track
- especially on minimum radius curves
- imagine a slow Festiniog-gauge line hundreds if not thousands of miles long.
Frequency counts of the above yet to be determined.
- "COUNTRY NEWS". The Argus (Melbourne, Vic. : 1848 - 1957). Melbourne, Vic.: National Library of Australia. 29 February 1864. p. 7. Retrieved 19 September 2015.
- "THE FESTINIOG RAILWAY". The Brisbane Courier (Qld. : 1864 - 1933). Qld.: National Library of Australia. 12 January 1870. p. 4. Retrieved 29 September 2015.
- "RAILWAY EXTENSION". South Australian Register (Adelaide, SA : 1839 - 1900). Adelaide, SA: National Library of Australia. 27 November 1867. p. 2. Retrieved 26 August 2015.
- "THE FESTINIOG RAILWAY". The Hay Standard and Advertiser for Balranald, Wentworth, Maude...(Hay, NSW : 1871 - 1873; 1880 - 1881; 1890 - 1900). Hay, NSW: National Library of Australia. 16 April 1873. p. 2. Retrieved 4 October 2015.
- "MUNDOORAN". Australian Town and Country Journal (Sydney, NSW : 1870 - 1907). Sydney, NSW: National Library of Australia. 25 November 1871. p. 7. Retrieved 14 September 2015.
- "RAILWAYS IN TASMANIA". Launceston Examiner (Tas. : 1842 - 1899). Tas.: National Library of Australia. 7 December 1869. p. 1 Supplement: Supplement to the Launceston Examiner. Retrieved 26 October 2015.
- "The Little Old Railway". The Sunday Herald (Sydney, NSW : 1949 - 1953). Sydney, NSW: National Library of Australia. 18 February 1951. p. 11 Supplement: Sunday Herald Features. Retrieved 28 October 2015.
- "Advertising". South Australian Register (Adelaide, SA : 1839 - 1900). Adelaide, SA: National Library of Australia. 28 July 1888. p. 2. Retrieved 30 November 2015.
Dow A (2014) The Railway, British track since 1804, Pen & Sword, 47 Church Street, Barnsley, South Yorkshire, S70 2AS, UK