(aviation) zero-zero, a term meaning no ceiling and no visibility

Under the Whyte notation system, a steam locomotive that is articulated in three parts, with a boiler mounted on the centre frame, and two steam engines mounted on separate frames, one on each end of the boiler, and each having an 0-4-0 wheel configuration.

Under the Whyte notation system, a Garratt steam locomotive that is articulated in three parts, with a boiler mounted on the centre frame, and two steam engines mounted in opposite directions on separate frames, one on each end of the boiler, and each engine having a 2-6-0 wheel configuration.

Under the Whyte notation system, a Garratt steam locomotive that is articulated in three parts, with a boiler mounted on the centre frame, and two steam engines mounted in opposite directions on separate frames, one on each end of the boiler, and each engine having a 2-8-0 wheel configuration.

plural of 2-8-0+0-8-2

plural of 2-6-0+0-6-2

plural of 0-4-0+0-4-0