In addition to the Light Mikado, the USRA standard designs also included the heavier variant, which basically had the same running gear. However, it received larger cylinders and a significantly heavier boiler. Although similarly sized Mikados were still being built without a stoker at the time, USRA locos had one as standard. The largest customer was Milwaukee Road, which took 100 units and designated them as Class L3. By 1922, a total of 233 original USRA standard design Heavy Mikados had been built. A further 724 copies were built by 1944, based directly on the design. 