Chris,
Though the spares list says "sprocket", that included the hub and flange as shown in the drawing. For the average owner ordering parts, describing it as a sprocket was more identifiable than calling it a clutch disk center.
The ohv models used a double sided friction plate of Ferodo linings. They also required a pressure plate, usually visible by the two or three drive pegs sticking through the face of the flywheel. I am not sure if they used a single sided Ferodo disk in the thirties on the big side valve models, usually you see the cast aluminum friction plate with the cork inserts. Different story with the 250-350cc models. Those did use a single sided Ferodo clutch disk.
-Doug