The BB18¼ class locomotive was a type of 4-6-2 steam locomotive operated by the Queensland Railways. The locomotives operated on 1067 mm (3 ft 6 in) gauge. The “B” is used to identify the number of coupled wheels being six coupled wheels for the BB18¼ class followed by numerals indicating the cylinder diameter of 18¼ inches. These new locomotives were classed BB18¼ to distinguish them from their predecessor the B18¼ class.
