 They were purchased in quantity by the Denver, South Park & Pacific Railroad.Unlike the Forneys, the Mason Bogies were actually articulated locomotives, whose boilers and fuel/water tanks were on the main frame and the engine was on a steam truck (hence the name "bogie") articulated to pivot beneath the boiler.Because the steam truck was articulated, the reach rod and reversing lever was positioned above well above the main frame earning the locomotives the nickname "sewing machines."