Early Y-Block distributors were vacuum only units referred to as Load-o-matic. These distributors  picked up a vacuum signal from the carburetor and varied advance based on engine demand. The Load-o-matic distributors will not work with modified engines! Usually the early distributors have metal tags to identify the part number. When the cap is removed the advance springs are visible. These distributors were used from 1954-1956. 1956 4bbl. cars used a dual diaphragm advance unit.

Beginning in 1957 centrifugal advance was added. The body of the distributor is thicker and the springs are no longer visible with the cap removed. The rotor can be turned and will then spring back to it's static position. Part numbers are stamped into the body . These distributors used a full diameter breaker plate which rotates on ball bearings. The vacuum advance arm is straight. Points cap and rotor will not interchange with the '54-'56 distributors.

About 1959 the ball bearing breaker plate was replaced with a hinged plate which pivots on a single pin. The vacuum advance arm is curved. These units use the same points, cap and rotor as the '57-'59 units and later 289-302.

12127 is the identifier for a distributor. The last two digits indicate actual application.

YEARS                      PART NUMBER

1957-59                    FEK  or  FEH       12127      Ball bearing breaker plate

1959                        B9AF  or B9TF     12127     Hinged breaker plate

1960                       C0AF  or C0TF      12127                  "

1961                       C1AF  or  C1TF     12127                  "

1962                       C2AF  or C2TF      12127                  "

1963                       C3TF                  12127                   "

1964                      C3TF                   12127                   "

Late and service replacement distributors use the 289 style triangular body with o-ring seal.

Not all of these numbers may actually exist.