About: 0-6-6-0

Under the Whyte notation for the classification of steam locomotives, a 0-6-6-0 wheel arrangement refers to a locomotive with two engine units mounted under a rigid locomotive frame, with the front engine unit pivoting and each engine unit with six coupled driving wheels without any leading or trailing wheels. The wheel arrangement was mostly used to describe Mallet locomotive types. A similar wheel arrangement exists for Double Fairlie, Meyer, Kitson-Meyer and Garratt articulated locomotives, but on these types it is referred to as 0-6-0+0-6-0 since both engine units are pivoting.