2-6-6

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