Boxpok -- a proprietary name for the General Steel Castings design -- were the most commonly used disc driving wheels on late American steam locomotives, but the Baldwin Locomotive Works had its own type: recognizable from the raised "lips" around the openings and, if you get a good view, from the words "Baldwin Disc Driver" cast on the face of the driver center. I think they were broadly comparable in physical characteristics. Baldwin drivers were used in a number of locomotives of the late 1930s -- Santa Fe Hudsons and Northerns, for example -- but a reasonable number of late Baldwins, notably the (production) T1 duplexes for the Pennsylvania -- had Boxpok. Is there some (known and interesting) reason why they used Boxpok instead of their own version on these late locomotives? (The obvious thought is that there was a cost advantage. But -- given the collapse in the market for steam locomotives in the 1940s -- I would have thought that Baldwin would have had plenty of capacity at their own foundry, so I would be surprised if they were unable to produce in-house driving wheels as cheaply as they could buy them from a subcontractor.)
Hmm… I ***think*** General Steel Castings was a joint subsidiary of Alco and Baldwin. And one of its foundries was in… Eddystone, PA. So maybe the financial aspects are a wash: buying from GSC is close to being an internal sourcing for BLW. (??? I'm sure more could be said about this by someone who knows more than I do!)
With regard to the Pennsylvania Railroad's T-1… The prototypes, 6110 and 6111, built in 1942, had Baldwin Disc Drivers: very recognizable in photographs, given the lips around the openings and an additional ridge op the middle between any two openings. The production series, built in 1945, had Boxpok. So maybe BLW decided, during the war, that it wasn't worth while trying to sell their own model of disc driver in competition with Boxpok?
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The PRR T-1 is what made me think about the issue: the December 2015 issue of "Railfan and Railroad" has a two-page article by spokespersons of the Pennsyvania Railroad T1 Steam Locomotive Trust, the organization that is trying to build a new T-1 (inspired by the successful British project to build an all-new locomotive to a 1945 design). Their project has apparently gotten to the stage of making a wooden pattern for casting new Boxpok drivers, and the reference to Boxpoks made me wonder why a BLW locomotive wouldn't have had BDDs instead of Boxpoks.