The "Duomatic" may also be a Sachs two speed coaster brake hub. There are two types. One is a kickback two speed, where shifting is accomplished by doing a "kickback" with the pedals. The other was a true automatic that would shift once the hub was spun at a certain RPM. "Duomatic" seemed to maybe have been a trademark for one or both of these types of hubs by Sachs.