S Scale Model Railway Society

Turnouts are generally referred to in the UK by combining their Switch types (for example A, B, C) and their crossing angle, (for example "1 in 4" or "1 in 6”) to give a name such as A4 or B6. Prototype turnouts are built up wherever possible from standard units, the vee crossing and the switches. Closure rails link these units to complete the formation. The dimension from the toe, that is the tip of the switch blade, to the nose of the crossing is referred to as the “lead” of the turnout.

The radius of a turnout will never be greater than that of the switch radius. If a finer angle of crossing than standard is required a straight length of closure rail is inserted at the crossing end. When the switch and turnout radii coincide the turnout is referred to as “natural”. A sharper than natural turnout will have two radii, whilst a larger than natural turnout (for example a B10) will have a straight insert in the closure rails.

Modellers are advised to obtain photographs wherever possible of the type of formation that they wish to build.

Railway companies used different methods of arranging the long 12 ´ 6 inch sleepers. Some companies placed the timbers at right angles to the main route but the Great Western together with a few others located their timbers at right angles to a centreline drawn through the crossing vee. The “A” switch was not used by the GWR.

Switch Type	Prototype Turnout radius	“S” gauge Turnout radius		Prototype Lead	“S” Gauge Lead		Remarks
	(feet)	(inches)	(metres)	feet ins	(inches)	(mm)
Switch Rail radius 482’-0” (90.375”) in S scale. Switch rail length 20’-0” (3.750” in S scale)
A4	130	24.375	0.619	42’-8”	8.000	203.2
A4½	168	31.500	0.800	44’-10”	8.406	213.5
A5	212	39.750	1.010	46’-10”	8.781	223.0
A5½	264	49.500	1.257	48’-9”	9.141	232.2
A6	326	61.125	1.553	50’-7”	9.484	240.9
A6½	398	74.625	1.895	52’-4”	9.812	249.2
A7	482	90.375	2.296	54’-0”	10.125	257.2	Natural Turnout
A7½	482	90.375	2.296	54’-2”	10.156	258.0	Straight section
A8	482	90.375	2.296	54’-7”	10.234	260.0	Straight section

Switch Rail radius 613’-0” (114.937”) in S scale. Switch rail length 22’-6” (4.219” in S scale)
B6	312	58.500	1.486	56’-8”	10.625	269.9
B6½	374	70.125	1.781	58’-10”	11.031	280.2
B7	445	83.437	2.119	60’-10”	11.406	289.7
B7½	524	98.250	2.496	62’-9”	11.766	298.9
B8	613	114.937	2.919	64’-7”	12.109	307.6	Natural Turnout
B9	613	114.937	2.919	65’-2”	12.219	310.4	Straight section
B10	613	114.937	2.919	66’-6”	12.469	316.7	Straight section

Switch Rail radius 960’-0” (180.000”) in S scale. Switch rail length 28’-6” (5.344” in S scale)
C7	416	78.000	1.981	68’-11”	12.922	328.2
C7½	485	90.937	2.310	71’-0”	13.312	338.1
C8	562	105.375	2.677	73’-1”	13.703	348.1
C9	740	138.750	3.524	77’-1”	14.453	367.1
C10	960	180.000	4.572	80’-9”	15.141	384.6	Natural Turnout
C12	960	180.000	4.572	82’-5”	15.453	392.5	Straight section

Switch Rail radius 1379’-0” (180.000”) in S scale. Switch rail length 28’-6” (5.344” in S scale)
D8	545	102.187	2.596	80’-2	15.000	381.0
D9	707	132.562	3.367	84’-7”	15.879	403.3
D10	896	168.000	4.267	88’-11”	16.672	423.5