In the late steam era, to improve balancing, many railroads replaced their locomotives' spoked driving wheels with disc driver centers of several types — the Boxpok ("box-spoke"), Baldwin, or Scullin types. However, it was rare to find older and smaller locomotives so re-equipped. One exception was the St. Louis Southwestern, or "Cotton Belt," which applied Scullin drivers to its class G-0 Ten-Wheelers built by Baldwin in 1916, represented here by No. 667. These engines were the mainstays of the Cotton Belt's passenger service, weighing 222,000 pounds and producing 33,389 pounds of tractive effort. They had 69-inch drivers, 200 p.s.i. of boiler pressure, and cylinders measuring 22x28 inches. As a whole, members of this class had a grate area of 49½ square feet, an evaporative heating surface of 2474 square feet, and a superheating surface of 532 square feet. No. 667, however, was one of two rebuilt with Nicholson thermic siphons in the firebox, which reduced the amount of evaporative heating surface but increased the amount of direct heating surface. All members of the G-0 class, originally coal burners, were converted to burn oil. Wesley Krambeck recorded No. 667 at Memphis, Tennessee on August 8, 1940 in a photo purchased from an eBay vendor.