The B&O's "Big Six" group of 2-10-2s featured 220 p.s.i. of boiler pressure and 30x32-inch cylinders, and their 64-inch drivers were so well counterbalanced that they proved to be faster locomotives than the typical "drag freight" 2-10-2 of their era. They weighed 436,000 pounds and mustered 84,150 pounds of tractive effort. Their evaporative heating surface totaled 5250 square feet, with 1510 square feet of superheater surface, and they had a grate area of 88 square feet. Robert Leffingwell snapped this transparency of No. 512 (original number uncertain, but between 6133 and 6140) at the B&O facility in Garrett, Indiana on March 21, 1957. No examples of this famous design have been preserved.