0-4-4-2

In Whyte notation for the classification of steam locomotives by wheel arrangement, an 0-4-4-2 is a locomotive that has no leading wheels, two sets of four driving wheels and two trailing wheels.

Equivalent classifications
Other equivalent classifications are:
 * UIC classification: BB1 (also known as German classification and Italian classification)
 * French classification: 020+021
 * Turkish classification: 22+23
 * Swiss classification: 2/2+2/3

Examples
0-4-4-2Ts were the first-generation mallets used by Indonesia since colonial time, back in late 19th to early 20th century by Staatsspoorwegen as state railway company of the Dutch East Indies ordered 12 units from Hartmann and the rest of 4 from Schwartzkopff in 1899–1908, classified as SS Class 500 (501–516) and used for winding mountain line in West Java. These locomotives worked for mixed trains that transported crops, plantations and passengers on Buitenzorg–Bandung line which opened in 1884. These oil-burned engine had power output of 465 hp (horse power) which way more powerful and suitable for tackling the winding mountain terrain with agility, compared to older SS locomotives the 2-6-0T (SS Class 300 or DKA C11 and SS Class 400 or DKA C12) which are smaller and slower in size and engine power. The SS 500s were also worked at Rangkasbitung and Banjar. From 16 of them, only BB10 12 (ex-SS 512) is preserved now. The SS Class 500 has specifications with its length is 10,5 metres, 1050 mm wheel diameter, weighing 44,1 tons and has a maximum speed of 50 kilometres per hour (31 mph). During Japanese occupation in 1942, these locomotives were renumbered to BB10 and used on Saketi–Bayah railway construction which was used as Japanese war effort for coal transports to the southern coast of West Java as from coal mining in Cikotok. This line was also known as "Death Railway" due to its construction using Japanese PoWs and local residents which were known as romusha or force laborers. One of the BB10 (number 05) was used on Indonesian struggle theme movie titled "Lebak Membara" (1982) produced by Sabirin Kasdani which tells the story about Indonesian fighters during the Japanese occupation. The last mallets were built for Indonesian Railway (DKA) were 4 units of Type BB1n4v by Nippon Sharyo or known as BB80 class (81–84) came in 1962 for narrow gauge (750 mm) railway line in Aceh. The line itself was built in 1876–1917 by Atjeh Tram which was a part of Staatsspoowegen tram division. The BB80s becoming the last Mallets built in the world and the only mallets that were manufactured in Asia. From 4 of them only BB84 is preserved as static display in Banda Aceh.