THE FAMOUS TRIPLEX MALLET, Matt H. Shay, of the Erie Railroad, U.S.A. Once the largest locomotive in the world, this engine of the 2-8-0 + 0-8-0 + 0-8-2 type, can haul loaded freight trains over a mile long. The diameter of the six cylinders is 36 in. and exceeds the length of the piston stroke, which is 32 in.