2-6-6

ALCO-built 2-6-6 suburban tank locomotive of the New York Central and Hudson River Railroad.

In the Whyte notation for describing steam locomotive wheel arrangement, a 2-6-6 is a locomotive with a two-wheeled leading truck, six driving wheels, and a six-wheeled trailing truck. All the locomotives produced of this arrangement have been tank locomotives, and the vast majority in the United States. It was a popular arrangement for the larger Mason Bogies, as well as some of the largest suburban tank locomotives.

Other equivalent classifications are:
UIC classification: 1C3 (also known as German classification and Italian classification)
French classification: 133
Turkish classification: 37
Swiss classification: 3/7

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v • d • e Steam locomotive types

Single engine types	0-2-2 • 2-2-0 • 2-2-2 • 2-2-4 • 4-2-0 • 4-2-2 • 4-2-4 • 6-2-0 0-3-0 0-4-0 • 0-4-2 • 0-4-4 • 2-4-0 • 2-4-2 • 2-4-4 • 4-4-0 • 4-4-2 • 4-4-4 • 4-4-6 0-6-0 • 0-6-2 • 0-6-4 • 2-6-0 • 2-6-2 • 2-6-4 • 2-6-6 • 4-6-0 • 4-6-2 • 4-6-4 0-8-0 • 0-8-2 • 0-8-4 • 2-8-0 • 2-8-2 • 2-8-4 • 2-8-6 • 4-8-0 • 4-8-2 • 4-8-4 • 4-8-6 • 6-8-6 0-10-0 • 0-10-2 • 2-10-0 • 2-10-2 • 2-10-4 • 4-10-0 • 4-10-2 0-12-0 • 2-12-0 • 2-12-2 • 2-12-4 • 4-12-2 • 4-14-4

Duplex engine types	4-4-4-4 • 6-4-4-6 • 4-4-6-4 • 4-6-4-4

Garratt (articulated) types	0-4-0+0-4-0 • 2-4-0+0-4-2 • 2-4-2+2-4-2 • 4-4-2+2-4-4 • 0-6-0+0-6-0 • 2-6-0+0-6-2 • 2-6-2+2-6-2 4-6-2+2-6-4 • 4-6-4+4-6-4 • 2-8-0+0-8-2 • 2-8-2+2-8-2 • 4-8-0+0-8-4 • 4-8-2+2-8-4 • 4-8-4+4-8-4

Mallet (articulated) types (includes Triplex)	0-4-4-0 • 0-4-4-2 • 2-4-4-2 0-6-6-0 • 2-6-6-0 • 2-6-6-2 • 2-6-6-4 • 2-6-6-6 • 2-6-8-0 • 4-6-6-2 • 4-6-6-4 0-8-8-0 • 2-8-8-0 • 2-8-8-2 • 2-8-8-4 • 4-8-8-2 • 4-8-8-4 2-10-10-2 • 2-8-8-8-2 • 2-8-8-8-4

Engerth (articulated) types	0-4-4 • 0-4-6 2-6-2 • 0-6-4 • 0-6-4-0 0-8-4 • 0-8-6