Accellerator pump for Ford Motorcraft 1bbl rebuilt carburetor. For all model 1100 Autolite and Motorcraft carburetors found on Mustand 6cylinder engine. SOme of these carbs will require 2 of these Ford diaphragms. 1 will be the accelerator pump and the other is the dashpot. Ford replacement part covers C3AZ-9B559-A. A must have part to cure hesitations in your Ford 1bbl carburetor.