As others have mentioned, the item is a governor; more specifically, a "sandwich" governor, as it is sandwiched between the carburetor and the intake manifold. Other manufacturers of sandwich governors of which I am vaguely aware are Handy, Hough, and King-Seeley.
All of the major carburetor companies (Carter, Holley, Rochester, Stromberg, and Zenith) also had carburetor models with integral governors; that is, the governor was part of the carburetor.
Governors were activated by a variety of controls. Holley used on various models, water pressure and oil pressure. Stromberg used oil pressure. Carter, Rochester and Zenith used vacuum. There are probably others.
Jon
