This information applies to all track standards: ScaleSeven, O fine and O coarse. It is based on Midland Railway drawings c. 1875-1890, but is believed to be reasonably representative of main line railways of the time. Since trackwork lasted a long time, it is likely to apply to most of the 20th century also.

The geometry of a straight switch is shown in Figure 1.


Figure 1. Geometry of a straight switch.

The prototype heel clearance h_c from the stock rail is 1¾in or 1.02mm in 7mm scale and this dimension can be used for ScaleSeven, giving a heel divergence of 2.62mm when using 1.6mm wide rail. For O fine scale, h_c is 1.75mm and for O coarse scale, h_c is 2.2mm. The heel divergence h_d is obtained by adding the rail head width h_r, to h_c.

The switch dimensions and timbering for the range of switches suitable for most modelling are shown in Figures 2 to 5. Timber dimensions are based on pre-grouping practice and are 10in. wide × 9ft. long (5.8mm × 63mm) and 12in. wide × 9ft long (7mm × 63mm). The prototype thickness for the 10in. timbers was 5in. and 6in. for the 12in. wide timbers. All dimensions are in millimetres.


Figure 2. 6ft Tongue switch.


Figure 3. 9ft Tongue switch.

For a heel switch, the switch rail is 58.4mm long with a mean timber spacing of 18.7mm and with the heel on the centre-line of the timber.


Figure 4. 12ft Tongue switch.

For a heel switch, the switch rail is 79.3mm long with a mean timber spacing of 15.7mm and with the heel on the centre-line of the timber.


Figure 5. 15ft Tongue switch. For a heel switch, the switch rail is 100.3mm long with a mean timber spacing of 16.6mm and with the heel on the centre-line of the timber.

This article was compiled by M. Holland for the Gauge O Guild Manual. It was adapted for the GOGWiki by Nick Baines.