 A distinguishing feature of the locomotive was the high-set N class boiler, which was pitched above the frames to accommodate the inside cylinder assembly, potentially exposing the conjugation mechanism to the elements.To prevent corrosion, Maunsell incorporated a vertical metal cover above the front buffer beam to protect the inside cylinder and valve gear assembly, the main visual difference from the N class.Maunsell and Holcroft anticipated that the standard N class chimney would choke the exhaust blast produced by the three cylinders.