In such cases, subcontractors were hired to build to PRR designs, unlike most railroads that ordered to broad specifications and left most design choices to the builder. The Pennsy's favorite outsourced locomotive builder was Baldwin Locomotive Works, which received its raw materials and shipped out its finished products on Pennsy lines. The two companies were headquartered in the same city; Pennsy and Baldwin management and engineers knew each other well. When the Pennsy and Baldwin shops were at capacity, orders went to the Lima Locomotive Works in Lima, Ohio. Only as a last resort would the Pennsy use the American Locomotive Company (Alco), based in Schenectady, New York, which also built for Pennsy's rival, the New York Central. The Pennsylvania Railroad had a design style that it favored in its locomotives. One example was the square-shouldered Belpaire firebox. This British-style firebox was a Pennsy trademark that was rarely used by other locomotive builders in the United States. The Pennsy also used track pans extensively to retrieve water for the locomotive while in motion. Using this system meant that the tenders of their locomotives had a comparatively large proportion of coal (which could not be taken on board while running) compared to water capacity. Locomotives of the Pennsylvania had a relatively clean look to them. Only necessary devices were used and they were mounted neatly on the locomotive. Smoke box fronts bore a round locomotive number board denoting a freight locomotive or a keystone number board denoting a passenger locomotive. Otherwise the smoke box was uncluttered except for a headlamp at the top and a steam-driven dynamo generator behind it. In later years the positions of the two were reversed, since the generator needed more maintenance than the lamp. Each class of steam locomotive was assigned a class designation. Early on this was simply a letter, but when these ran short the scheme was changed so that each wheel arrangement had its own letter, and different types in the same arrangement had different numbers added to the letter. Sub-types were indicated by a lower-case letter; super-heating was designated by an "s" until the mid-1920s, by which time all new locomotives were super-heated. A K4sa class was a 4-6-2 "Pacific" type (K) of the fourth class of Pacifics designed by the Pennsy. It was super-heated (s) and was of the first variant type (a) after the original (unlettered). Steam locomotives remained part