3 mm scale

3 mm scale, also known as 3 mm finescale, is a model railway scale of 3 mm : 1 ft (305 mm) used for British prototypes. Introduced as British TT gauge, it sits approximately halfway between British N gauge and OO gauge but is not as popular as either and there is no longer any mass manufacturer ready-to-run support. When TT gauge model railways were developed for British prototypes, in order to fit the small British prototypes, the scale was enlarged but without altering the 12mm gauge. The result, British TT gauge, is too narrow. This led to the development of 14.2 mm (0.559 in) gauge 3mm finescale. Thus two finescale standards were developed. By far the more common of these is 14.2 mm gauge track, which is accurate. Some modellers choose to use slightly narrower 13.5 mm track due to the necessary oversize motion of outside-cylindered steam locomotives.

3 mm finescale
Scale	3 mm to 1 ft (305 mm)
Scale ratio	1:101.6
Model gauge	9 mm (0.354 in) (3' gauge) 13.5 mm (0.531 in) (Scotch) 14.2 mm (0.559 in) (standard) 15.75 mm (0.620 in) (Irish) 16.5 mm (0.65 in) (Indian) 21 mm (0.827 in) (Brunel)
Prototype gauge	3 ft (914 mm) 1,372 mm (4 ft 6 in) (Scotch gauge) 1,435 mm (4 ft 8+1⁄2 in) (standard) 5 ft 3 in (1,600 mm) (Irish gauge) 1,676 mm (5 ft 6 in) (Indian broad gauge) 2,134 mm (7 ft) (Brunel gauge)
Website	http://www.3mmsociety.org.uk/

British TT gauge
Scale	3 mm to 1 ft (305 mm)
Scale ratio	1:101
Model gauge	12 mm (0.472 in) TT gauge
Prototype gauge	Standard gauge

British TT, also known as TT3, was pioneered by Triang Railways as ready-to-run models.

Other gauges are also used to model other prototypes (Irish broad gauge, Brunel gauge). For narrow gauges, N gauge 9 mm track represents 3 ft (914 mm) gauge; Z gauge 6.5 mm (0.256 in) track represents to 2 ft 2 in (660 mm) gauge.

The 3mm Society caters for all modellers of 3 mm scale.

See also

• Rail transport modelling scales
• Model railway scales

External links

• 3mm Society
• 3mm Supplier