The New York Central System designated its 4-6-0s, or Ten-Wheeler type dual service locomotives, as class F. The locomotive shown here was a member of class Fx, outshopped by the American Locomotive Company in 1906-07 and formerly owned by the Ulster & Delaware, absorbed by the New York Central in 1932. The letter "X" was used to indicate that the members of the group — which varied from one another in various dimensions and in details such as valve type or the placement of appliances — were not otherwise differentiated by subclass. They had 62-inch drivers and weighed 176,500 pounds. With a boiler pressure of 200 pounds per square inch and cylinders measuring 20x26 inches, they developed 31,440 founds of tractive force.

No. 40 retained its Ulster & Delaware number for several years after the U&D became the New York Central's Catskill Mountain Branch. To differentiate them from NYC H10 2-8-2s in the same number series, the Ten-Wheelers of Class Fx were lettered "CMB" below the number on the cab. In 1936 both the Fx and H10 classes were renumbered and this No. 40 became No. 817. According to Steve Delibert, president of the Ulster & Delaware RR Historical Society, the former No. 40 probably never ran anywhere except on the former U&D, so this photo must have been taken somewhere between Kingston and Oneonta, New York. Members of class Fx survived to the end of NYC steam in the East, and No. 40 / 817 was again renumbered to 1230 shortly before being scrapped in 1949.