Primer Bulb MTD 951-10639A OD: 1 5/8" OD 1 5/8" Height 1" Ethanol Not compatible with greater than 10% ethanol fuel Included in the 520-866 Carburetor 520-866 Carburetor, Included in the 520-864 Carburetor 520-864 Carburetor, Included in the 520-852 Carburetor 520-852 Carburetor, Included in the 520-856 Carburetor 520-856 Carburetor