A 4-4-6, in the Whyte notation for the classification of steam locomotives by wheel arrangement, is a locomotive with: * four (4) leading wheels (at the front of the locomotive) * four (4) driving wheels (2 axles) fixed in a rigid frame, and * six (6) trailing wheels (normally mounted in a trailing truck). An example of this wheel arrangement was the Thuile locomotive. Other equivalent classifications are: * UIC classification: 2B3 (also known as German classification * Italian classification), and * French classification: 223.