Here there was a retrograde step taken in gear design, because the gear ratio of Type N at left is 69/19 and of Type M at right is 78/16. As a result, Type M's teeth would develop a wear pattern a little sooner than those of Type N. The hub of Type M's main gear is a little stronger than that of Type N's. The frames show quite a bit of chenge in layout, though the basic patterns are the same insofar as support of the two gears is concerned. The outer faces of both main gears are smooth - Type M's was machined, Type N's was not.